Posted By: 
Tim NewcombSorry I didn't see this post when it cropped up over the holidays.  I won't go into huge detail here, as I don't want to anticipate all of Bob's and my material for the projected article-- 
but i will correct a couple of misapprehensions expressed in the post:
-- the "300 Subjects" backs appear on the cards from Series 19-24, not 22-24.  There are thus 72 players that appear only with this back. There are some anomalies concerning this back and certain lower-series cards, which I'll get into later. 
-- I believe all 19-24 series cards are scarce to some degree.  However, it appears that possibly 15-20% of them are somewhat less scarce than the rest.  The less scarce cards don't correspond neatly to any of the numerical series.  We're working on a theory of reissues that accounts for this.  But I don't think it's right to call any of the 19-24 groups "commons".  They are all definitely short-printed cards.  
Tim