Could be that they simply didn't know who wrote it From Wikipedia: "When the recording appeared on their 1969 debut album, the credit read "Traditional, arr. by Jimmy Page" following the unspecified (at the time) authorship of the track on Baez's album. In the 1980s, Bredon was made aware of Led Zeppelin's version of the song; since 1990, the Led Zeppelin version has been credited to Anne Bredon, Jimmy Page, and Robert Plant. Bredon received a substantial back-payment of royalties."
BoozyB 2 points 2 days ago
Could be that they simply didn't know who wrote it
From Wikipedia:
"When the recording appeared on their 1969 debut album, the credit read "Traditional, arr. by Jimmy Page" following the unspecified (at the time) authorship of the track on Baez's album. In the 1980s, Bredon was made aware of Led Zeppelin's version of the song; since 1990, the Led Zeppelin version has been credited to Anne Bredon, Jimmy Page, and Robert Plant. Bredon received a substantial back-payment of royalties."