Every disc on the RCA label, it's subsidiaries, and indeed the myriad of independent labels which utilised it's mighty mastering and pressing facilities, feature a letters and numbers. During the mid-60's they had four recording hubs of New York, Chicago, Hollywood or Nashville. Their codes can be broken down thus:
As an example I'll use the code "634P-0987". The '634P' is the account number of the client, or the info for the company / person who initialised the account. It has nothing to do with arriving at a release date. The second number '0987' is simply the master number referencing the tape used to make the master.
The other part of the code that is included on independent labels pressed by RCA, as well as the major label itself, is the code which reads as, -e.g. "TK4M-0987". Once again, the second set of numbers refer to the master tape reference number, but the first part of the FOUR DIGIT CODE tells us the following -
Noted by the first letter - see below.
K = 45rpm if there was an L = 7" 33 1/3 rpm; R = 12" 33 1/3 rpm; P = 10" 33 1/3 rpm
(An EP actually retained the 'K' in the third position, while 'B' in the fourth position was mono and 'A' was stereo.)
THE TYPE OF ACCOUNT:
A '4' = Custom - re-recorded from client's furnished tapes -i.e. the client recorded at their own venues, then took the tapes to any of the RCA studios which then cut the lacquers.
A '5' = Custom job whereby the lacquer was furnished to RCA -i.e. cut at a non-RCA studio.
"M" denotes mono, "S" would denote stereo.
In the example TK4M-0987, the "T" denotes a 1966 year of mastering and not always the actual year of release, but it usually is accurate 95% of the time and is a useful rule of thumb. The RCA year codes are thus -
L - 1960 / M - 1961 / N - 1962 / P - 1963 / R - 1964 / S - 1965 / T - 1966 / U - 1967 / W - 1968 / X - 1969
Z - 1970 / A - 1971 / B - 1972 / C - 1973 / D - 1974
One can then pin-point the disc further, as if the account number, in this case "4", falls BEFORE the "K", then the disc was mastered between January and June of 1966. If the number is after the "K", as in our example TK4M, then it was mastered between July and December, 1966.
In addition to the above, most independent label releases also have a letter stamped into the dead wax which indicates which plant was used -
R - Rockaway, New Jersey,
I - Indianapolis, Indiana, (50 miles Northeast of Bloomington at 7900 Rockville Road)
H - Hollywood, California.
Finally, during 1966, their Chicago studios were apparently so busy that their last set of numbers put the number (3/4/5) in the first position and the year in the second (4TKM!). And as to the period up to 1962, the second position was 7, 8 or 9 (indications same as 3, 4 or 5, respectively, post-1963), 'O' was their code for "Phonograph," and 'W' denoted a 7", 45 RPM release. (i.e. L7OW, M9OW or NO8W).