[nolemmings]

1981 is a good demarcation. I stopped collecting new stuff in 1994 and frankly don't recall when the move first went to inserts/chase cards as in fancy holograms/foils/refractors, then inserts such as autographs, then game used inserts then retro (old cards included in new card packs). Are more than one of these worthy of their own distinction and demarcation?

'73 is a nice debate, but it wasn't exclusively a single series release for everyone, as that appears to have been a test to see what they would do going forward. So I'd be more inclined to look at '74 as the first decidedly single release year..

That's fine David, everyone has an opinion and after this I'll stop beating my dead horse. IMO, 1973 was key for three reasons: production, set composition and distribution. Production: It was the first time that the cards were all printed and ready to go by late December early January; i.e. before any Spring player moves. Prior to that, you could still count on some of the high number cards to reflect late moves. Not so as of 1973.

Set Composition: 1973 was the first set to reduce the set size by a significant number of cards and settle on what would become a standard set size of 660 cards for five years. Also the 1973 composition was the first to dedicate a significant number of the player's standard/main cards to action photos, taking a road that would never lead back.

And yes, distribution. It was the first set to be issued all at once, rendering series meaningless. You say it was a test. I propose that leaving the cards in series one last year was the test, and/or that this was done to hedge against distribution problems with jobbers at the regional and local levels. OPC was distributed all at once in 1973. So was Topps football. Clearly the decision had been made and there was no reason to await "test" results. The article shared by Howie in another thread concerning the then upcoming 1973 baseball card set contained a statement by a Topps exec that the majority of the country would be receiving the cards all at once, which of course sounds much different than a test. It may in fact have been distributed in this fashion to much of the nation--the evidence is unclear. There was no reason to issue the cards in series, given that there were no upgrades or differences from those who got them all at once. A good portion of the country had entire sets assembled while others waited for so-called high numbers. In sum, the commitment by Topps to go all at once started in 1973 and for this and the other reasons turned a page in card collecting history IMO. Maybe not as noticeable a demarcation as to what happened later, but noteworthy nonetheless.