finkleroy: Sorry about that. I wasn't told about any region restrictions with that key, so now we have to play the guessing game. Hooray! It doesn't count toward your limit, of course.
It may be worth considering marking all that donor's games as potentially region-restricted against the US at the very least.
For what it's worth I don't blame you or the donor (unless the key source specifically marked it somewhere, in which case it would seem fair to place blame on them for not giving you relevant info beforehand). You can't look at a key and somehow determine if it's restricted after all. It would be a pretty useful, if crappy, superpower to have though.