I can't speak for FM translators, but I know TV translators and LPTV stations don't actually have anything in the rules requiring coverage of the community of license. The logic behind this is that a translator may be in a sparsely populated unorganized area that doesn't have a named community, or an LPTV may cover just a portion of a community where a specific population lives. But it's how you end up with things like WASA-LD in New York, which is licensed to Port Jervis but doesn't even come close to covering Port Jervis anymore.
LPTV and TV translator stations can update their communities of license without any FCC permission, as a result. I think it just takes a license modification filing. But if the licensee hasn't bothered to update it, then it wouldn't change, of course.
- Trip