I'm not sure how well it'd work there, but I'd have to test it out. With limited testing (.txt file 'as-is') and multiple copies of the .xlt, it'll write to the .txt file anytime the book(s) is opened. That also means, even if you exit out of it and don't save it, you're still going to increment it by one. I guess this is a good reason why I'm a big fan of keeping everything in one place.

But, I haven't tested it too thoroughly yet.