globetrotters.us:
I would propose that houses that didn't have any formal documentation, just 'word of mouth' and a photo that matched one with formal documentation be allowed, with a disclaimer that said how it was derived. This way, there would be a starting point for someone with a real interest to do more research. It's easier to archive a waymark that proved to be wrong than to find something that only has an oral history.
I suppose there could be a variable for this, given enough evidence to make the waymark plausible to accept. The problem would be in order to view the variable for a waymark you have to open each one to see it. The undocumented homes would far outweigh those that have documentation and they would get lost in the mix. A sister category perhaps?