The Grand slammer with no line on back are only in the Cello jumbo packs. I got a bunch of the and opened them. To find that all the grand slammers in cello packs are without line. And the ones with a line are in the factory sets.
I saw you had said that you found different versions of the borders on the grand slammers. Did you notice that the ones with different borders don't have the black bar on the back?
Does anyone have the #18 Howard Johnson Diamond King with the line on front corner and the full number on the back. I am willing to buy that card from you. Me and my father spent three weeks going through all of our 1990 donruss to put a complete Master set with every error and variation in it...