I'd say in all cases I can think of - if you're doing (and claiming you are doing) a specific version, do it right. If you're doing your own version, or if you just don't care, do it however you feel happy with.

As to lyric sources? Once again - if it's a version with a stated source, try to get them correct. If not, who's to say WHAT version is the 'correct' one?

M