I think proper names have to be excluded, excepting eponyms and other terms that have the status of common nouns. “Kleenex” e.g.
Usually when I’ve played Scrabble the rule is that you pick a single dictionary to be the arbiter (hence my brother’s successful challenge of BOX–>BOXY: Webster’s Collegiate was a bit thin on adjectival forms, however common, grrrrr). But since this is the Interwebs I’d be happy to just stipulate Brian’s list. Point is it can’t be too open-ended or disputes go on for ever.