[drcy]

Scraps were sheets where the printing didn't come out right, so they were thrown away (scrapped) and someone figuratively or literally retrieved them from the trash can and hand cut the cards. The worker may have brought the sheet home for his kids.

Most scraps are handcut and have bad or missing printing. A lot of the psychedelic misprints, cards missing colors or terribly overlapping colors are scraps-- tossed away due to the bad printing. They often have blank backs but can have printed backs.

Most proofs offered for sale are actually scraps.

Scraps really only have extra value if the printing is especially unusual and striking. If entire colors are strikingly missing, such a card printed in only black and yellow, or the color alignment is totally off to the point of causing vertigo, that can bring a premium. I assume blank backs bring a premium. Otherwise, the card is just printing that didn't meet standards and should be valued less than a factory finished card.

I wouldn't surprised if factory cut blank backs made it into cigarette packs. Blank backs have been pulled out of Topps packs. I pulled a blank back out of a 1979 Topps pack as a kid.

Identifying proofs of cards is tricky. Sometimes they are on different stock and have crosses and marks so can be identified as such, while other times they look just like blank back misprints. I've had proofs from 1989 Gurnsey Topps Archive auction that looked just like regular blank back cards. The fronts were normal with all the printing. The only way I knew for sure they were proofs was Topps said they were. Other proofs from the same auction were clearly proofs just looking at them, as they were on very different stock (smooth bright white instead of the normal rough grey/brown Topps stock), blank backed and the fronts contained as few as one color and had no text. One proof had just the yellow ink.

The most interesting trading card proof I have is on transparent mylar sheets. Each sheet has a different color ink and when you put sheets on top of each other you get the finished design. It's clearly not a scrap.