Real name: Anne Loeb, married to Glen Bredon.
Joan Baez [for Vanguard on live lp In Concert with no credits; Joan picked it up at a hootenanny at Oberlin College hearing Janet Smith sing the song, who personally managed to straighten things right; re-releases do mention the author's name]
Plebs [first British cover on Decca]
Led Zeppelin [not crediting Brendon initially; see footnote]
Chicago [used elements from Led Zep's Babe I'm Gonna Leave You in their 25 Or 6 To 4]
CD reissues of the Led Zeppelin cover co-credit the real songwriter, thanks to the same Janet Smith, whose son kept wondering why his out-and-out folk mother sang a damned Led Zeppelin song over and over again. One claim addressed to Page & Plant settled the case. They only knew that In Concert album, where no author was mentioned, and assumed it was a traditional.