Back Sleeve Identifying Numbers & Letters - Jacket/Slick Printing Companies

WARNING: The numbers on the back of the jacket currently are only for Capitol Records & Subsidiaries (regular printed number), RCA and Columbia Records & Subsidiaries (regular numbers and block numbers). It would be inaccurate to assume other labels used these same facilities, so be careful! Also, in the description, my speculations are in there. these are not facts and should not be used as such. When they become verified, or backed up with evidence, I will put it in the list. I will make it clear if it's a theory or speculation. Feel free to message me with any questions, comments, corrections, evidence, or tips.

Background:
Capitol Records, RCA, and Columbia Records sleeves from the 1950-70's used outside companies to print their jackets and slicks. The outsourcing of jackets can be identified by numbers (and maybe letters) printed on the back bottom jacket, which correlate with the factory the vinyl was pressed at and the printing company, currently either Modern Album or Imperial Packing. Queens Litho, Bert-Co and sometimes Ivy Hill Lithograph printed the front cover jackets, which were trimmed for mono and stereo by the fabricator (modern or imperial). Queens & Bert did not put identifiers on the jackets so they are unable to be identified most of the time.
Spizer on Capitol Records Numbers: "Most of the back liners have a small numeral located near the lower right or left corner. These numbers were used by Capitol to identify where the album cover was manufactured. Capitol did not fabricate its own album covers*. Capitol required the cover manufacturer to place a factory identification number on the back liners. The fabricators added a small number, usually in the lower right corner." After speaking with Bruce, he noted that the fabricators (Imperial or Modern) were required to do this for quality control, most likely that if a slick or assembly of the entire sleeve was poorly done, the major label would know who did it. He also noted that the slicks on the back were made by the fabricators.

UPDATE - Per Bruce Spizer: It was never an "exact science" to relate the pressing plant with a number on the back. For instance, If an east coast pressing plant was used, it's likely that they used a New York fabricator, however midwest fabricators were also used due to demand, delays, etc. So, You cannot discern a pressing plant solely by the number on the back sleeve. Only the fabricator!

Currently unknown locations: 8 (Imperial, but don't know which one) and all numbers greater than or equal to 10.

Note: Odd numbers are Modern Album, and even numbers are Imperial, but the exact location is not known for 10 or greater. These most likely occur with extremely high demand records, but not always.

Currently Merging Companies and gathering info.: https://discogs.programascracks.com/forum/thread/1000859

References for numbers:
http://www.yokono.co.uk/collection/beatles/usa/lp/usa_lp.html
https://www.searchingforagem.com/CountryIndex.htm
https://www.friktech.com/btls/CoverNumbers.pdf (Please do not use, this is invalid information)
https://www.stoughtonprinting.com/history.html
https://londonjazzcollector.wordpress.com/record-labels-guide/columbia-records/columbia-matrix-codes-case-study-kind-of-blue/
https://londonjazzcollector.wordpress.com/record-labels-guide/columbia-records/columbia-cover-manufacturers/
http://pinkfloydarchives.com/Discog/US/LP/RDI.htm
Bruce Spizer directly.

Other Printed Codes:
Sometimes sleeves have GAM, CSC, ELT (example Ed Thrasher & Associates or whatever company Ed was working for prior to his own.
Waiting for help with these: https://discogs.programascracks.com/forum/thread/842619?page=1#8387883

Pressing Plant Identifiers (or unlikely in-house printing):
Some pressing plant identifiers: 6 B, S, A, & ♥ printed on the back sleeve currently indicate the location of pressing, but hopefully we can determine in there was a printing facility at these plants. 'S' was used for Santa Maria Pressings, 'A' was used for Terre Haute Pressings, and '♥' was used for Pitman Pressings. They seem to be on only Columbia labels. Example of "A": Dave Brubeck - Jackpot which has '3 and A'. After speaking with Bruce, he was not too knowledgeable about the S, heart and A, but he thought it was unlikely that they did their own printing. He said it's possible, because capitol tried it for a while, but he thought that it would have been cheaper to outsource the fabricator.

998-D has been observed on the back of Decca Records, particularly ones pressed at Lenny Dee (2) - Moving On)

Branches of Modern Album:
• New York:(Parent Company) Modern Album Finishing Co. Fabricator codes 1, 3
• New Jersey: Modern Album Of New Jersey Inc.
• Indiana: Modern Album, Terre Haute, Indiana: Fabricator codes 5, 7 & 9.
• California: Modern Album, Burbank
• Tennessee: Modern Album Of Tennessee
• Canada: Modern Album of Canada Ltd.
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