Just for clarity on all my responses in these threads, I'm a (minor) contributor to Nix the Tricks and a personal friend and research partner of the author.

Yes, all of the tricks were submitted by math teachers that we have seen used in practice. I don't think that we are all Americans, but a most of us are.

I personally haven't seen too many of them, especially the weirder ones, but I know they were not invented whole-cloth for the book.