The blank back versions were inserted into packs of Topps BIG. Notice that the blank backed cards do not have the "automatic entry into sweepstakes" disclaimer on the front (bottom left of card).
I am a collector of 1980's and 90's Topps Offer/Ad inserts and have been tracking these for many years. There are scarce versions of the 1988 and 1989 cards but they have to do with the card stock they were printed on and so, very few collectors seem to care about them.
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