Thought of counterfeit, but style doesn't match any I can find in my collection (have 5,300 or so left, 80+% all betwn '88-'94); you're right that it resembles 1990 Topps - though it wouldn't have been very 'smart' to copy the back info from the year after the 90 sets were printed lol; + the green is primary solid whereas all Topps' regular sets that year had slimmer borders in assorted 2-tone pastels from colors of the basic rainbow. The Topps' inset trim lines were always side/top of 1 primary color & side/bottom of another (the red/yellow on my mystery card are parallel reds/yellows and thinner than the 'legit' cards - stock on the mystery actually better quality & sturdiness than the late80s, early 90s as well..
Oh well, will probably remain unsolved forever - just bugging me since it doesn't match anything else I've seen or remember. . thanks for the reply Sportzcommish!