Just received a splendid packet of 1,000 worldwide aviation topicals. I rediscovered a common feature that I recalled from my youth (1970s) - that is, there's a lot of stamps bearing cancellations that remain fully gummed on the reverse. Strictly speaking, they are not "postally used." Pending your response, I'm guessing that such stamps are the product of smaller nations that print, gum, and cancel stamps expressly for philatelic markets. Your thoughts?
Cancelled to order (CTO). And not just by the usual suspects - the Aussies have been doing this (albeit on better quality material) for 120 years. A less attractive development has been the printing of the actual cancel on the stamp.
Sweating stamps off (stamp lift box) will or can leave the gum intact but it usually changes the gum's, appearance. I made a large sweat box out of a cooking pan to un-stick mint full panes that I got from an estate sale while ago. It worked but I consider them "disturbed gum".