In baseball,
1991 Bowman (print sheet VAR on some cards)
1987-1992 Donruss (everything from reversed back orientation, font differences, INC dot or no dot, etc.)
1990-1992 Fleer (U.S.A. or U.S.A; 1991 has font variations consistent with the U.S.A. VAR)
1992 Leaf base and black gold (INC dot or no dot)
1991-1992 Stadium Club - (print sheet variations)
1988-1990 Topps Big (print sheet variations on some cards)
1990 Topps Traded (* or ** by copyright)
1991 Topps (dark logo variation)
1994 Topps (some don't have the print sheet letter identifier)
1990 Upper Deck (some missing copyright line)
1991 Upper Deck (hologram VAR)
I am sure I missed some; someone will add to this list.
Bruno
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Check my Profile page to see my 2023 Goals and my Lists of sets near completion (5 cards or less) or sets getting close (less than 100 cards missing and 75% complete).
https://www.tcdb.com/Forum.cfm/Page/B/ID/0/?MODE=VIEW&ThreadID=25745&C=0