https://www.net54baseball.com/showthread.php?t=184284
Found this thread from 10 years ago - some interesting observations on this subject.
It is clear that some areas received cards by series and others "all 660" without overlap. It is also clear that all 5 series were printed by the end of 1972, eliminating any same-year spring training pics which used to be traditional in hi series cards.
As to the checklists, from what I can read here it seems like recollections are all over the place - only in 660 packs, only in 5th series packs, all year long, late in the year.
The thread mentions a good article on the set by Bill Haber - the link is long dead it seems. If anyone has that article, could you post?