I'd be surprised if he couldn't, or if he didn't have his own documentation somewhere in a notebook that he's using for an ashtray.(I have no idea if Satoshi smokes and presume that he doesn't)
Personally, when working on an open source project, I find it hard to believe that any documents relating to the protocol could cause any sort of dispute over their authorship, especially when we have such fine resources as Creative Commons.  I don't think anyone would have any problems with that.