@notesaddict: That is the beginning of the code: S for Stereo, A for Atlantic. Then Numbers. Then a suffix. The suffix on the Atlantics, usually a two letter code, is the pressing plant, e.g. MO is Monarch.
Not saying those are the best, just one factor among many including who mastered the record. Those are usually inscribed in the deadwax. If you look up info on Atlantic deadwax inscriptions, you'll see a ton of stuff.
