You see them listed in recording session books and scribed in the lead-out grooves of LPs - but what exactly are they?
It's a long standing mystery which I am now going to try to explain.

This is the matrix number coding system used since 1963. Before 1963 some codes had different meanings which are explained later.

First though, you need to know what the letters and numbers mean:

1955 = F

1956 = G

1957 = H

1958 = J

1959 = K

1960 = L

1961 = M

1962 = N

1963 = P

1964 = R

1965 = S

1966 = T

1967 = U

1968 = W

1969 = X

1970 = Z

1971 = A

1972 = B

1973 = C

1974 = D

1975 = E

1976 = F

1977 = G

1978 = H

1979 = J

1980 = K

1981 = L

1982 = M

1983 = N

1984 = O

1985 = P

1986 = R

1987 = S

1988 = T

1989 = U

1990 = V

1991 = W

1992 = Z

1993 = A

1994 = B

1995 = C

1996 = D

1997 = E

1998 = F

1999 = G

2000 = H

2001 = J

2002 = K

2003 = L

-

-

-

Second Character
(Type of release)

Third Character
(Tape size and speed)

Fourth Character
(Description of the release)

C = RCA Camden
()

A = Master Tape
()

A = EP Stereo
()

A1 = RCA New York
(also Webster Hall)

N = Premium, Promotion
()

K = 7 inch 45 rpm
()

B = EP Mono
()

A2 = RCA Chicago
(Mid-America Rec. Center)

P = Popular
()

L = 7 inch 33 1/3 rpm
()

M = Mono
()

A3 = RCA Hollywood
(Music Center of the World)

I = International
()

R = 12 inch 33 1/3 rpm
()

S = Stereo
()

A4 = RCA Nashville
()

W = Country and Western
()

A5 = Recorded in the USA
(Not RCA studio)()

3 = Hollywood (Temporary)
()

A6 = Recorded outside of
USA

'A' in the third position of master tape serial numbers signified RCA; for labels RCA distributed, the code was B.
For example, 'Sugar Sugar' by The Archies, recorded in early 1969 at RCA's New York studios and released on the Calendar label
which later in '69 changed its name to Kirshner, bore a master serial number of XYB1-3908.

In the case of Elvis, he never recorded at any of RCA's Chicago studios (either 445 Lake Shore Drive pre-1969 or 1 North Wacker Drive from 1969-73), so this is why we see no Elvis sides with A2 in the third and fourth positions of master serial numbers.

RCA's Hollywood studios - located at 6363 Sunset Boulevard after 1963, and before that from 1959 at 1510 North Vine Street - assigned master serial numbers to the bulk of his film sides up to 1967. (For example, while Elvis recorded 'Relax' at Radio Recorders on September 22 1962, the master serial number PPA3-2726 was assigned by RCA Hollywood sometime in early 1963). Whenever tracks with such codes were released on 45, the third and fourth characters were supplanted by KM for mono 45s and KS for stereo 45s.

A1 was seen on many Elvis sides recorded between mid-to-late 1967 and late 1968, indicating that the master serial numbers with this code were assigned by, as well as mixed and edited at, the New York studio which, before 1969, was located at 155 East 24th Street in Manhattan (somewhere Elvis hadn't set foot in since 1956). Webster Hall, which RCA also used for sessions in New York, was on
East 11th Street.

In addition, such numbers were usually assigned a few months after Elvis committed the songs to tape, whether at a film studio or, say, Western Recorders in Hollywood.

However, the system of matrix numbers has changed several times and when you're looking at and comparing matrix numbers you'll see that RCA doesn't always apply its own rules.

This leads to the next point, based on what has been seen of sessions by other artists (ranging from Perry Como to The Archies), namely, exactly when these master serial numbers were assigned. I have a guesstimate based on such other sessions.

- WPA1-1001 and 1002 / 1022 - 1030, and 1038 and 1039 (Speedway tracks) were apparently assigned in New York in the early
months of 1968;
- WPA1-5766 - 5769 (from Live A Little, Love A Little) were assigned around August 1968;
- WPA1-8023 - 8050 (NBC-TV Special) were assigned around mid-to-late October 1968;
- WPA1-8091 (Charro) was assigned in November 1968;
- WPA1-8111 - 8125 and 8135 were assigned either November or December 1968; and,
- XPA1-3976 - 3978 (around the time of The Trouble With Girls) were assigned within the first few months of 1969.

Some label discographies (e.g. Michel Ruppli's on US Decca Records) have made such indicators in sessions for British artists, mentioning a UK session date and then below in parentheses "(master numbers assigned in NYC, [date here])". I presume if a date on any documents pertaining to these sides existed, that would be the date they were assigned.

If anyone can clarify this discrepancy, I would appreciate it.

The pre-1962 code listing is as follows:

Second Character (Label Description)

Third Position (Type or Description)

The changeover in 1963 coincided with the first full year of the existence of the label's infamous "Dynagroove" recording process.

Prior to 1962 (the last year RCA used codes which were first put into effect in the calendar year 1955 as signifying their "New Orthophonic High Fidelity"), EP codes were signified by an "H" in the fourth position on mono 45s and "Z" in the fourth position on stereo 45s. ("R" in the third position up to 1962, and in the second position after 1963, indicated a "Red Seal" classical release.)

As for other second characters pre-1962, "7" indicated a custom recording made at RCA studios and "8" and "9" indicated a custom job whose tape was provided to RCA for mastering at any one of their studios.

This was usually followed in the third position by a letter "O" (erroneously listed by some printing companies that did label copy for RCA as a number "0" zero) which was classified as Phonograph (such as G7OH for a 1956 custom EP, or GO7H if assigned later in the year).

The matrix number for 'Heartbreak Hotel' is G2WB-0209 and is made up of the following:-
G = 1956
2 = RCA Victor commercial popular music release
W = Country and Western
B = Mono 78 rpm (20-6420)
0209 is the next in line from the set of numbers RCA assigned to Elvis for this session.

For the 7 inch mono 45 rpm release of 'Heartbreak Hotel' (47-6420) the matrix number is G2WW-0209. For the EP 'Heartbreak Hotel'
(EPA 821) it must have been considered to be "Popular" rather than "Country & Western", as the third letter was changed from "W" to "P" (G2PH)

For this initial session of January 10/11 1956, eleven numbers were assigned to Elvis for recording eleven songs (0208 – 0218). It was probably envisaged by Steve Sholes that they would record an album and a single, but with only five songs recorded it must have seemed like a disaster.
G2WB-0208 - 'I Got A Woman'
G2WB-0209 - 'Heartbreak Hotel'
G2WB-0210 - 'Money Honey'
G2WB-0211 - 'I'm Counting On You'
G2WB-0218 - 'I Was The One'

The missing matrix numbers between 'I'm Counting On You' and 'I Was The One' have been shrouded in mystery over the years, some even indicating (or more likely hoping) that the missing numbers were for unreleased songs recorded by Elvis during this session. The fact is that the unused numbers were later assigned to other artists:
G2WB-0201 - 'Wonderful' (Blackwood Brothers)
G2WB-0202 - 'What Would You Do' (Porter Wagoner)
G2WB-0203 - 'How Can You Refuse Him Now' (Porter Wagoner)
G2WB-0204 - 'Tryin' To Forget The Blues' (Porter Wagoner)
G2WB-0205 - 'Uncle Pen' (Porter Wagoner)
G2WB-0206 - 'How I've Tried' (Porter Wagoner)
G2WB-0207 - 'I Like Girls' (Porter Wagoner)
G2WB-0208 - 'I Got A Woman' (Elvis)
G2WB-0209 - 'Heartbreak Hotel' (Elvis)
G2WB-0210 - 'Money Honey' (Elvis)
G2WB-0211 - 'I'm Counting On You' (Elvis)
G2WB-0212 - 'Annabelle' (Poppa John Gordy)
G2WB-0213 - Unknown (Poppa John Gordy)
G2WB-0214 - 'Lookout Mountain' (Otto Bash)
G2WB-0215 - 'Later Aligator' (Otto Bash)
G2WB-0216 - 'Moritat' (Theme from Three Penny Opera) (Poppa John Gordy)
G2WB-0217 - Unknown (Poppa John Gordy)
G2WB-0218 - 'I Was The One' (Elvis)
G2WB-0219 - 'Have Mercy On You' (Country Pardners)
G2WB-0220 - 'Maple On The Hill' (Country Pardners)
G2WB-0221 - 'Another Old Dog In The Race' (Country Pardners)
G2WB-0222 - 'Ever-Ready Kisses' (Country Pardners)

Matrix numbers were usually assigned weeks in advance of recording sessions and were for a set number of songs to be recorded. If an additional song was recorded at a session the matrix number for it had to be from the next batch of free numbers available, and if fewer songs were recorded than were planned then the spare matrix numbers had to be reused elsewhere.

However, there are also some very interesting things you can find out while digging around in these matrix numbers.

With the song 'I Want You, I Need You, I Love You', although it was announced as G2WB-0270 during the recording session and can be heard with this announcement on the outtakes of the song, it should be 0271 because G2WB-0270 was already assigned to Jim Reeves for the song' I've Got Just The Thing For You' recorded on April 11 1956.
G2WB-0268 - 'My Lips Are Sealed' (Jim Reeves)
G2WB-0269 - 'Pickin' A Chicken' (Jim Reeves)
G2WB-0270 - 'I've Got Just The Thing For You' (Jim Reeves)
G2WB-0271 - 'I Want You, I Need You, I Love You' (Elvis)
G2WB-0272 - 'Your Wild Life's Gonna Get You Down' (Carol Johnson)
G2WB-0273 - 'I Haven't Got The Right' (Carol Johnson)
G2WB-0274 - 'According To Law' (Carol Johnson)
G2WB-0275 - 'Let Him Go, Step Aside' (Carol Johnson)

This also explains why 'I Want You, I Need You, I Love You' was listed in RCA's session logs (and all discographies until the mid-1990s)
as being recorded on April 11 1956 when, in fact, it was recorded on April 14. It was G2WB-0270 that was recorded on April 11,
not G2WB-0271!!!

During Elvis' October 30/31 1960 recording session, a block of thirteen matrix numbers were allocated for Elvis to record thirteen songs (0373 to 0385), but as Elvis recorded an additional song ('Working On The Building'), so the matrix number for that song had to be assigned from the next available batch of numbers (5001):
L2WW-0373 to 0385 (Elvis)
L2WP-0386/0387 - Souvenirs (Hank Snow - mono LP)
L2WY-0388/0389 - Souvenirs (Hank Snow - stereo LP)
L2WP-0390/0391 - Tall Stories & Short Tempers (Jim Reeves - mono LP)
L2WY-0392/0393 - Tall Stories & Short Tempers (Jim Reeves - stereo LP)
L2WP-0394/0395 - Songs My Mother Never Sang (Homer & Jethro - mono LP)
L2WY-0396/0397 - Songs My Mother Never Sang (Homer & Jethro - stereo LP)
L2WP-0398/0399 - Unknown LP-sides
L2WY-0400/5000 - Unknown LP-sides
L2WW-5001 - 'Working On The Building' (Elvis)
L2WW-5002 - Unknown Title (Floyd Cramer)
L2WW-5003 - 'Too Young' (Floyd Cramer)

Another occasion where Elvis recorded an additional song and where a matrix number had not been assigned was during the May 26/27 1963 recording sessions. For the session on May 26 eight matrix numbers were allocated (0290 – 0297), and for May 27 five matrix numbers were allocated (0302 – 0306) for Elvis' use, but Elvis recorded fourteen songs in total instead of thirteen!

PPA4-0284 - Medley (Stepin' Fetchin')
PPA4-0285 - Bossa Nova Twist (Stepin' Fetchin')
PPA4-0286 - 'Shake, Rattle And Roll' (Stepin' Fetchin')
PGA4-0287 - 'Push A Little Harder' (Avons)
PGA4-0288 - 'I've Got More Love' (Avons)
PGA4-0289 - 'Oh Gee Baby' (Avons)
PPA4-0290 to 0297 (Elvis)
PPA4-0298 - 'Mama, You'd Have Been Proud Of Me' (Dottie West)
PPA4-0299 - 'Let Me Off At The Corner' (Dottie West)
PPA4-0300 - 'That's Where Our Love Must Be' (Dottie West)
PPA4-0301 - 'Didn't I' (Dottie West)
PPA4-0302 to 0306 (Elvis)
PWA4-0307 - 'Little Black Book (Jeanne Pruett)
PWA4-0308 - 'Back To Her Arms Again' (Jeanne Pruett)
PWA4-0309 - 'Sing Me A Song I Can Cry By' (Jeanne Pruett)

As had happened before, with the song 'I Want You, I Need You, I Love You', on May 27 1963 'Blue River' was announced as 0307 during the recording session, although that number had already been assigned to Jeanne Pruett for the song 'Little Black Book'.
This mistake must not have been realised until 1965 when 'Blue River' was first intended to be released, as it was then issued with a new matrix number SPA4-6768. It is interesting to note here that the SPA4-6768 matrix number is for the unedited Take 2 of the song, which was not released! However, to make 'Blue River' longer for release, it was spliced from 0:00 -1:25 and 0:44 -1:31 of Take 2 and this was issued yet another matrix number, SPA4-7357 in 1965. It was this which was released as a single, and later on the 'Double Trouble' album.

There are some matrix numbers where there is no information available, including some from around the time of the sessions for 'Blue Hawaii' in 1961 and some from around the time of the sessions for 'Girls! Girls! Girls!' in 1962.

From 1965 there is another matrix number for which there is no information - SPA4-5389. This dates from around the time an overdub session was held in 1965 for 'Tomorrow Night' (included on the album 'Elvis For Everyone'). I can only assume that this matrix number could be for 'Wild In The Country' with overdubbed maracas, which was used instead of 'Summer Kisses, Winter Tears' on European pressings of that album, although the matrix number of the European pressings for side 1 of the LP was S2PP-9101 for the mono LP and S2PS-9102 for the stereo LP.

SPA4-5389 - 'Wild In The Country' (maracas overdub)?
SPRM-5390/5391 - 'Elvis For Everyone' (mono LP)
SPRS-5392/5393 - 'Elvis For Everyone' (stereo LP)
S2PP-9101 - Side 1 of 'Elvis For Everyone' (European matrix number for mono LP)
S2PS-9102 - Side 1 of 'Elvis For Everyone' (European matrix number for stereo LP)

The above theory does actually make sense considering that it is normal for the album matrix numbers to directly follow the matrix number of the last song recorded for an album, and, in this case, 'Wild In The Country' may have been dropped from the song line up in favour of 'Summer Kisses, Winter Tears'.
For example, the matrix mumbers SPA3-2001 to SPA3-2011 were for songs recorded for 'Girl Happy'
- the last song being 'I've Got To Find My Baby'.
SPA3-2011 - 'I've Got To Find My Baby'
SPRM-2012/2013 - Girl Happy (mono LP)
SPRS -2014/2015 - Girl Happy (stereo LP)

Matrix numbers SPA3-6751 to SPA3-6761 were for songs recorded for 'Harum Scarum'
- the last song being 'My Desert Serenade'.
SPA3-6761 - 'My Desert Serenade'
SPRM-6762/6763 - Harum Scarum (mono LP)
SPRS-6764/6765 - Harum Scarum (stereo LP)

Matrix numbers SPA3-7374 to SPA3-7385 were for songs recorded for 'Frankie And Johnny'
- the last song being 'Everybody Come Aboard'.
SPA3-7385 - 'Everybody Come Aboard'
SPRM-7386/7387 - Frankie & Johnny (mono LP)
SPRS -7388/7389 - Frankie & Johnny (stereo LP)

Looking at the January 1968 recording sessions reveals a gap in the matrix numbers which, over the years, fans thought could have been unreleased songs recorded by Elvis. In fact, the missing numbers are for songs by Jimmy Dean recorded on January 17 1968.
WPA4-1800 - 'Too Much Monkey Business' (Elvis)
WWA4-1801 - 'Read 'Em And Weep' (Jimmy Dean)
WWA4-1802 - 'A Rose Is A Rose Is A Rose' (Jimmy Dean)
WWA4-1803 - 'A Thing Called Love' (Jimmy Dean)
WWA4-1804 - 'She's Mine' (Jimmy Dean)
WWA4-1805 - 'It'll Be Easy' (Jimmy Dean)
WWA4-1806 - 'When It's Sleepy Time Down South' (Jimmy Dean)
WPA4-1807 - 'U.S. Male' (Elvis)

The master matrix number of 'I'll Be Home On Christmas Day' (remake) is incorrectly listed as APA4-1296 in RCA's session logs
whereas it should be APA4-1297.

When the session tapes were rediscovered in the 1990s the confusion was explained. The original master reel had 'My Way' listed as APA4-1296 and 'I'll Be Home On Christmas Day' (remake) listed as APA4-1297 and it was found that RCA's original engineer had changed the number on the session log after the event, indicating that Elvis and/or Felton Jarvis had decided that 'My Way' wasn't worthy of release. Therefore, a matrix number wasn't assigned to 'My Way' originally in the session logs.

Finally, the matrix number of a record can also be used to identify and work out the release date of the record.
As an example, for years, discographies have incorrectly listed the EP 'Christmas With Elvis' (EPA 4340) along with the LP 'Elvis' Christmas Album' (LPM 1951), which was a re-release of the 1957 issue of 'Elvis' Christmas Album' (LOC 1035) with new cover, as being released in September and November 1958, respectively. However, the September 1958 date is actually impossible for the EP, not just because there is a picture of Elvis taken in May 1959 on the cover (which also includes pictures taken in 1959 on the LP cover), but because the matrix numbers for the EP (K2PH-2461/2462) were not assigned until April 1959. If the EP had been released in 1958 it would have had a matrix number starting with J2PH (J = 1958 / K = 1959). You don't have to know when pictures were taken for an album cover to determine when it was released: the year of release of the record is there, scribed in the lead-out grooves of the record - if you know what you're looking at!

Finally, there are many other examples where discographies etc. have given the wrong year of release.
For example, the one-sided promo release of 'Old Shep' (CR-15) is still listed by some as being released in December 1956, even though the matrix number (H7OW-3721) was not allocated until May 1957 (H = 1957).

Also the 'WOHO Featuring' RCA Victor promo containing 'Old Shep' is still listed by some as being released in December 1956, even though the matrix number (J7OH-2287/2288) was not allocated until April 1958 (J = 1958).

The 'TV Guide Presents Elvis Presley' (G8MW-8705) from 1956 is still commonly listed as being an EP. But it wasn't!
If it had been an EP, the fourth letter would have been an "H".

I do hope I haven't bored everyone, but this is a subject which fascinates me. And, as you can see, a lot of surprises, as well as long lost answers, are revealed in these intriguing and mysterious numbers.

(Special thanks to Kurt Rokitta, Henk Muller and William Brown)