These are indeed RCA matrix codes. Here is partial information about RCA's code:

  The "E" stands for the decade in which the matrix was prepared: i.e., a year in the 1950s (E being the fifth letter of the alphabet). The "3" designates the year of the decade in which preparation took place: thus, 1953. I can help less about the following matrix information; it no doubt identifies the matrices partly as for an outside, non-RCA client, in this case Period. Others here will know more.

  RCA used this letter and number code to identify matrices for some time (thus D9 represents 1949, for example), but altered it after 1954 ("E4") and moved to later and later capital letters for each year.

  Don Tait





-----Original Message-----
From: Thomas Stern <[log in to unmask]>
To: ARSCLIST <[log in to unmask]>
Sent: Mon, Apr 8, 2013 4:37 pm

PMG 2001 has stamper numbers which look like RCA, none on 2003 except catalog 
  E3-DL-7562-1 / E3-DL-7563-1
Anyone have the key to decoding the RCA numbers ?????

The following is printed on the liner for 10" disks PMG 2001 and 2003.  I've not 
seen 2002.
 Many musical masterpieces, old and new, though they certainly deserve
to be available on records have not reached that stage because of their
supposed limited appeal and consequent limited sale. The Period Music
Guild has been organised for the purpose of producing on records  just
such music-works that regardless of their "connoisseur" standing or novel
quality are recommended or approved by the majority of the membership.
 This record is not a regular release of The Period Music Guild. It is
offered for the nominal sum of one dollar as a sample of the high quality
of performance and brilliance of reproduction of regular releases of
The Period Music Guild.  For further information concerning membership
write to--
PERIOD MUSIC GUILD   884 Tenth Avenue   New York 19, N.Y.  "

Thanks, Thomas.

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]]On Behalf Of Thomas Stern
Sent: Wednesday, April 03, 2013 9:43 AM
To: [log in to unmask]

Thank you Steve and Uncle Dave!

Can someone pinpoint the release dates - I have not found reviews or release 
in the few sources to which I have access.  Perhaps SCHWANN would have 
information, or if 
you know of other issues of these recordings on PERIOD and know those issue 
dates, that would give
an upper limit to the issue date on PMG.

BILLBOARD Dec 3, 1949 noted the start of Period:
PERIOD RECORDS Bows With Exclusive LP Policy
  A new diskery devoted exclusively to long-playing records has
set up its stand in New York.  Period Records, with Frank Stevens
as general manager, will specialize in longhair works, beginning with
the release of Charles Ives' "String Quartet No.2," played by the
Walden String Quartet, of Cornell University.  The next release will
be the abridged version of Tschaikowsky's opera "Eugen Onegin."
The latter disking was formerly issued on shellac by DISC Records.
Phoenix is the metropolitan distrib.

Online library catalogs list 1955? or 195? - I suspect they may have been
earlier, as 10-inch albums faded.

I've found listings of the following 3 PMG albums.

PERIOD MUSIC GUILD PMG-2001                                     10" LP  1955?
Program notes by B. Lebow on container.

CORELLI: Concerto grosso no.8 (Christmas concerto)
Vienna Chamber Orchestra; Anton Heiller, conductor.

also in PERIOD SPL 301 Showcase
        PERIOD SPL 540 Corelli/Vivaldi

PERIOD MUSIC GUILD PMG-2002                                     10" LP 1950?
"Exclusive edition"
notes by B. Lebow on container.

CHOPIN: Concerto no.1 in E minor, op. 11
Branka Musulin, piano; 
Sueddeutsches Rundfunk Symphonie Orchester; Hans Muller-Kray, conductor.

PERIOD MUSIC GUILD PMG 2003                                     10" LP 195- ?
Program notes in English on container.

PROKOFIEFF: Overture on Hebrew themes, op. 34
  Paris Chamber Orchestra
SCHUBERT: Quartetsatz in C minor
  Barchet String Quartet.

Best wishes, Thomas.

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]]On Behalf Of Steve Smolian
Sent: Sunday, March 31, 2013 11:08 PM
To: [log in to unmask]

Period Music Guild was a Period mail order operation- however brief.  The 
others are unconnected to it.

Steve Smolian

-----Original Message----- 
From: Thomas Stern
Sent: Sunday, March 31, 2013 8:24 PM
To: [log in to unmask]

Just noticed a couple of 10" LP releases on the PERIOD MUSIC GUILD label 
(PMG 2001, PMG 2003)
Trade mark as for PERIOD RECORDS.

There is also a MUSIC GUILD label, later issues from ABC records.

Is there any connection between the two labels (e.g. did Music Guild 
spin-off from Period, or ...) ???

How long did the PERIOD series last ????  Did Period evolve from Period 
Music Guild ????

Any information appreciated!

Thanks,  Thomas.