I obviously am not familiar with the software here but how about just labeling the entire set as VAR in the upfront description field and describing what's on the back in the VAR description field, anticipating the fact that there may well be multiple variations to ever number in the set?
Yes, you would wind up with some stickers with VAR (a) in the description and no VAR (b) but at least we'll be able to look and see what back is in the database for the one version that is entered. They are 30 year old sets after all and this situation is rather unique. I can see a few more variations being found (like mine, apparently) but is the volume of them really that high that adding them will be that large of a problem?
I'm in the all one set group. There's obviously a value difference between a Cal Ripken on the back as opposed to a B.J. Surhoff on the back (no offense, B.J.) and I'd like to see that connection reflected up front. Listing fronts and backs separately doesn't do that.