I'm not going to comment on this case directly, but there is no doubt that Led Zep borrowed heavily from other artists/songs in many of their songs; arguably a lot more than most bands of their stature.
Yes, there are influences and its sometimes difficult to say who copied what or what came first. But in their case, its happened again and again and again.
The truth is that musicians have been doing this for centuries. It used to be seen as a complement. There are a tremendous number of dimensions which can be copied/have influenced derived from them in any piece of music, and honestly the world benefits from this proliferation of musical ideas. If the artist had made something as good as what Led Zeppelin did, they would have profited from it, even if Led Zeppelin was able to profit from it as well. Intellectual Property rights in music hardly makes any more sense than Intellectual Property rights in software (and I think neither make sense).
"Babe I'm Gonna Leave You" - A folk song by Anne Bredon, this was originally credited as "traditional, arranged by Jimmy Page," then "words and music by Jimmy Page," and then, following legal action, "Bredon/Page/Plant."
"Black Mountain Side" - uncredited version of a traditional folk tune previously recorded by Bert Jansch.
"Bring It On Home" - the first section is an uncredited cover of the Willie Dixon tune (as performed by the imposter Sonny Boy Williamson).
"Communication Breakdown" - apparently derived from Eddie Cochran's "Nervous Breakdown."
"Custard Pie" - uncredited cover of Bukka White's "Shake 'Em On Down," with lyrics from Sleepy John Estes's "Drop Down Daddy."
"Dazed And Confused" - uncredited cover of the Jake Holmes song (see The Above Ground Sound Of Jake Holmes).
"Hats Off To (Roy) Harper" - uncredited version of Bukka White's "Shake 'Em On Down."
"How Many More Times" - Part one is an uncredited cover of the Howlin' Wolf song (available on numerous compilations). Part two is an uncredited cover of Albert King's "The Hunter."
"In My Time Of Dying" - uncredited cover of the traditional song (as heard on Bob Dylan's debut).
"The Lemon Song" - uncredited cover of Howlin' Wolf's "Killing Floor" - Wolf's publisher sued Zeppelin in the early 70s and settled out of court.
"Moby Dick" - written and first recorded by Sleepy John Estes under the title "The Girl I Love," and later covered by Bobby Parker.
"Nobody's Fault But Mine" - uncredited cover of the Blind Willie Johnson blues.
"Since I've Been Lovin' You" - lyrics are the same as Moby Grape's "Never," though the music isn't similar.
"Stairway To Heaven" - the main guitar line is apparently from "Taurus" by Spirit.
"White Summer" - uncredited cover of Davey Graham's "She Moved Through The Fair."
"Whole Lotta Love" - lyrics are from the Willie Dixon blues "You Need Love."
I've listened to both songs, and while there is a distinct similarity between Taurus and parts of Stairway to Heaven, they are not the parts that made the song memorable. Which is why one listen to Taurus is enough for a lifetime.
Yes, there are influences and its sometimes difficult to say who copied what or what came first. But in their case, its happened again and again and again.
Case in point: https://www.youtube.com/watch?v=ye2N_2ce3QE. There many more examples from Led Zeps music like this.
Massive Led Zep fan here, btw.