[drc]

Most blank back Topps were misprints that were inserted into packs and have the normal factory cuts. I pulled one or two as a kid.

The salesman sample uncut panels have the backs printed, so it wouldn't be from that. On salesman samples, any advertising is on paper pasted over the backs, and often to usually part of the backs is still showing.

A scap, handcut from a printing sheet certainly is a possibility.

Cut from other advertising sheet or related? I don't know. I don't know what advertising was used or is out there. Such an item most would probably be on a different stock than the regular cards, so that's an easy question to answer.