It could be a 1989. There is a 1989 set (not in our database) that is almost identical to the 1990 Classic set (fronts the same, numbering the same on most cards, text and copyright on back different). I see a 1989 Paul Roma on eBay with a blank back. The seller doesn't say why his is a blank back either (promo or whatever). I have never seen anything about blank backs when I have researched these cards in wrestling card forums. It's a very confusing set because the 1990 cards that came in foil packs have 1989 copyright dates, but not the cards from blister packs or factory sets. I haven't added this set just because it is so confusing and I don't have enough of them anymore to really be an authority.
I know this doesn't really answer your question, but it's the best I can do!
I'm going to reevaluate how I collect after the new year. It's just getting way too expensive for the new stuff. Sometimes I just want to buy a pack, not a whole box or even blaster.