From another forum page I was reading....
In 1963 another set of codes was introduced.
1st character (year recorded)
P: 1963/R: 1964/S: 1965/T: 1966/U: 1967/W: 1968/X: 1969/Z: 1970
(I have the other codes up to 1991 but I can’t be bothered to type those in
tonight. E-me if you need them.)
2nd character (label designation)
A: Grunt/B: TMI/C: Camden/D: Neon/E: Educational/F: Wooden Nickel/G: Groove/H:
Hugo & Luigi (1963-64), Chelsea (1972-73)/J: Children/K: Daybreak/L: Wheel/M:
George Jones Musicor masters (1972-73)/N: Various Artists/Promotional/P:
Popular/R: Red Seal/S: International/T: Gregar (1970-71) then Metromedia
(1972-73)/V: Victrola/W: Country & Western/X: Chart/Y: Calendar (later renamed
Kirshner)/Z: Colgems/1, 2: Readers’ Digest/3, 4: Custom (in-house disc
mastering)/5: Custom (outside disc mastering)
3rd character (size & speed)
A: master tape (also B, C)/K: 7" 45rpm/L: 7" 33rpm/P: 10" 33rpm/R: 12" 33prm
4th character (description)
A: stereo EP/B: mono EP/M: mono/S: stereo/T: quadrophonic/1: New York City
recording/2: Chicago recording (discontinued in 1973)/3: Hollywood recording/4:
Nashville recording/5: outside recording/6: foreign recording (?)