[Shouldabeena10]

Most of it is really "printers scrap" .. not proofs or anything done on purpose. Whenever a printer changes his printing plate or switches ink colors over they have to run off a bunch of scrap sheets to get the ink color built up completely, and to adjust the registration, centering, etc. It can sometimes take up to 30 or 40 sheets to get it right, and often you would use any leftovers from the last plate you ran to set up for your next run (that's where most wrong backs come from).

Also, whenever a customer orders say 1,000 sheets of something .. they always print a small amount of overages .. just in case. Especially if the job requires extra steps like cutting, because if the cutter messes some up you don't want to have to go back and reprint just 100 sheets again.

All those extra printed sheets are set aside onto a scrap pile. Some just sit there and pile up for decades. Some are reused. Some are used as top and bottom slip sheets when cutting the cards, because most older cutters would leave an impression mark in the first couple of sheets (from the clamp pressure) .. or may not cut all the way through to the bottom sheet if the blade was slightly dull.

If there was anything cool or unique (like sports cards) it wouldn't be unusual for a pressman to take a few sheets home for his kids to play with or hang up as a poster, etc. He may even cut a bunch of them up to give them to his kids, friends, etc.

I worked at print shops back in the 1980's and I still have a few weird things I took home from the shop.

A lot of the stuff that "The Topps Vault" ebay store sold as proof cards and color separation cards, etc. was just old cut up printers scrap. Because there's no earthly reason why they would print, cut and save all of those different variations.