Indeed though if a bunch of different users are doing it, you might want to allow it with a citation needed marker. I've been to so many articles with a "citation needed" marker for years, but surely it would not be too complex for someone to find a source.
Actually, that's not the purpose of [citation needed]. Adding a death date without a reference is very close to violation of [[WP:BIO]]. When I created [citation needed], I didn't envision it to be used for just adding any old data or information into articles, especially this sort of thing.
