The top one is a corner clipped from a postcard (Scott # UX9) issued in 1894. There were 250,000 of these issued. I don't know value, but it is collectible.
Unused UX9 has a catalog price of $40, used is $80 per the 2022 Scott US Specialized. The problem is that for envelopes a cut square is priced as well as the entire envelope with the cut square being less expensive. The issue for postal cards is that there is no normal catalog price for a cut square as such are not listed. For these higher cost postal cards, a cut square is collectible.