I do not think this is a "cut square" (i.e., stamp preprinted on envelope/card). Rather, the example shown is an actual stamp on cover that has been cut from the original cover. This stamp had die-cut perforations. If you look at the scan again, you will see how the NV postmark disappears slightly at the edge of the stamp before reappearing on the cover. Therefore, I believe this is an actual stamp, not postal card. That's what it looks like to me, anyway.

k