This is actually a study in judicious cropping. Indeed, SPQR hit on part of it by suggesting these are cut out of souvenir cards (although I didn't physically cut them out). Most of them are from cards, but the first four are from vignette panels in the American Bank Note Archive Series. From 1987-1992 ABNC produced six different portfolios containing 12 panels each; a different ink color was used every year. The panels typically featured 6 to 10 engravings on a particular theme. Many panels included reprints of stamps from the original plates.





Some of the cropped stamps are also from souvenir cards produced by ABNC, like the first one James posted. The others are from cards printed by the Bureau of Engraving & Printing. Early on, the BEP either used plates with a stamp's denomination removed or, for USPS souvenir cards, they enlarged the stamp design by 150% or more. Later, they began running a "cancellation" line through stamps reprinted in the original size and color. But during the mid-2000s they decided reprinting actual stamp designs in a different color was enough and left off the black lines. The 5˘ 1907 Jamestown reprint (Scott 330) is a surprise, though, as it was printed in blue ink like the original.




So what's the point to all this? Well, it didn't take too long for some shady dealers to begin chopping up these cards and panels and selling the individual engravings as "proofs." As you can see, many of the stamps provide ample margins so that, when carefully cut, they do resemble a die proof. These tend to sell for $10 to $30 apiece and up, which makes the panels especially tempting to cut apart. I've seen the two China "proofs" posted above sell for more than $200 each, and on one occasion more than $300. You can often purchase an entire portfolio (12 panels) for that price.
Probably the most prolific seller of this type of material on
ebay is cvcc-inc. If you check his sold listings in the Stamps category you'll see what I mean; they are usually listed as "Mint, Never Hinged" with no other details. It pays to be informed.
https://www.ebay.com/sch/Stamps/260...c-inc&_sac=1