To answer your question, when the print run for the album sleeve is made, be aware that a flip back is a two piece construction, as seen above on image #21174. The front laminated sleeve shown at image #21173 differs from the stereo version by having mono printed at top right, and vice versa. (I would imagine that the same print bed is used for both versions, and then mono & stereo are added later).
The date code visible at the bottom of the flip back 'rear' is purely for the printers info. in my opinion, and as you know includes the printers name, and reference to both mono and stereo versions with the catalogue numbers. It does not serve any other purpose, so if a later press of a vinyl album is made, any unused LP sleeves if still available, showing their original date of printing are married to the newly pressed vinyl.
That would explain why you have The Temptations album, probably with TM/EMI paper labels, but the original 1967 album sleeve. I have explained before, as I have worked for two record companies in the past, that album/single labels and to a lesser extent LP/EP sleeves are printed in larger numbers than vinyl , which can be pressed at short notice to meet demand.
You only have to take a look over on 45cat at EP sleeves, to be aware of the myriad re-printings of popular titles, some only a month or two apart. I'm sure that any competent printer would always add the correct printing code to a new print run for their product, although, as you'll know, some did not add dates.
Hi YankeeDisc, are you sure that the date code changed with later pressings? I have a 1970's pressing of THE TEMPTATIONS GREATEST HITS (STML 11042) in a non-flipback cover printed by Garrod & Lofthouse, still showing the code 6702 for February 1967, which is the original release date shown in the Davis book.
It certainly looks like code 6606 on the rear sleeve, together with printers name Ernest J. Day & Co. Ltd. London.
June 1966 seems feasible for a release date, although there may be others around with a later printing date, but I'm guessing not earlier. Also available in stereo on STML 11029.
Juniors' next album "Road Runner" TML 11038/STML 11038 came out in UK December 1966 (6612), printed by Garrod & Lofthouse Ltd. There may be variants.
The discography in Sharon Davis' MOTOWN: THE HISTORY gives the release date as June 1966. There might well be a date code of 6606 in the bottom right of the back cover, but it;s hard to tell from the scan.