Thanks guys, pms incoming!
Yea, I suspect I'll never find a Buster Douglas manual, and that's ok. In fact, I'm ok just having the games and if I can find missing manuals down the line, even better.
I only just recently thought to make a post like this as I've finished my US SMS collection, except for Sonic. I have a complete Sonic on it's way now from merry ole England (where it was cheaper than what US sellers wanted) and since it's identical in every way to the US version except for that UPC sticker, it will suit me perfectly. Essentially completing my SMS collection after about 15 years!
Now the big question - just how bad does Sonic play on Master System??