The notion of a “first” pressing is somewhat misleading in this case. Based on the other factors (dynaflex and/or the Motown ad as record sleeve) and information from other sources it would appear that most, even all, the lacquers were cut at roughly the same time.
Even though the TS-310 pressing with the ‘D’ in the matrix is not dynaflex, I do have a copy with the Motown ad which seems to indicate an earlier pressing. Not sure when the ads stopped so this is not definitive proof.
One knowledgeable source indicated that the dynaflex was used in the earliest pressings (see 1st thru 4th lacquers below) and as the oil crisis faded thicker began to be used sometime circa 1975. It's possible, though not expressly clear, that the 'C' and 'D' pressings can be dated to a later time. Still waiting for some details to surface on this.
One knowledgeable source indicated that the dynaflex was used in the earliest pressings (see 1st thru 4th lacquers below) and as the oil crisis faded thicker began to be used sometime circa 1975. It's possible, though not expressly clear, that the 'C' and 'D' pressings can be dated to a later time. Still waiting for some details to surface on this.
Not sure how distribution channels worked either. Would these have started in Indianapolis and then, due to demand, more lacquers were cut to keep up? In other words, the lacquer with no lacquer was used up before an 'A' lacquer was cut? This doesn't seem likely.
It would appear that multiple lacquers were cut based on geography and were distributed at the same time to meet pent up demand. One of the Motown engineers from that time has indicated that multiple lacquers were cut within a short period of time (within hours) from each other.
No matter what the answer is it quickly became, and remains, one of Motown's biggest sellers so none of these lacquers is what I would call rare. When I began this little project, I was able, within a short period of time, to track down a copy of each variation on ebay.
"Earliest" pressing is somewhat relative in this case so I will refrain from using "first pressing" but will instead refer to the lacquers as identified by the letter in the matrix.
1st lacquer* – TS-310, A4RS-2482-2 on Side 1; A4RS-2484-2 on Side 2; pressed at RCA’s Indianapolis plant; dynaflex vinyl
2nd lacquer* – TS-310, A4RS-2482-2-A on Side 1; A4RS-2484-2-A on Side 2; pressed at RCA’s Indianapolis plant; dynaflex vinyl
3rd lacquer – S-310, A4RS-2482-2-B on Side 1; A4RS-2484-2-B on Side 2; pressed at RCA’s Hollywood plant; dynaflex vinyl
4th lacquer - S-310, A4RS-2482-2-C on Side 1; A4RS-2484-2-B on Side 2; pressed at RCA’s Hollywood plant; thicker vinyl
5th lacquer - TS-310 or T-310, A4RS-2482-2-D on Side 1; A4RS-2484-2-D on Side 2; pressed at Southern Plastics (?); thicker vinyl
* There is some variation here. In other words there is no letter at the end of the matrix on Side A and there is an 'A' at the end of the matrix on Side B. This may be a separate lacquer altogether which would make a total of 6 lacquers. Not sure how the process of making these lacquers worked so can't say for sure but either way both were cut and pressed at the Indianapolis plant.
Thanks!