Page is the only guy that came out of the Yardbirds.....Zepplin is much harder music....and they may have lifted from those guys but they gave them songwriting credit where it was due.....
the Blues men plagiarized each other just as openly as the Brits did.
you will have to show me examples.....Willie Dixon songs were Dixon songs....same with Robert Johnson,Elmore James....there were a few that were disputed because no one was sure who wrote them.....that was just a few.....i googled that and could not find anything.....so its up to you.....and according to the semi-documentary on the Blues on PBS which i saw on one of their pledge drives a few weeks back.....the early Blues record Companies owned many of the songs....Willie Dixon who was well aware of song theft formed his own publishing company in 1957 to protect his copyright interest in his own songs........
Zeppelin was initially named "The New Yardbirds." Page was reforming the band,
As for plagiarism, be serious;
{
Noted blues author and producer
Robert Palmer states "It is the custom, in blues music, for a singer to borrow verses from contemporary sources, both oral and recorded, add his own tune and/or arrangement, and call the song his own".
[3] Folklorist Carl Lindahl, refers to these recycling of lyrics in songs as "floating lyrics". He defines it within the folk-music tradition as "lines that have circulated so long in folk communities that tradition-steeped singers call them instantly to mind and rearrange them constantly, and often unconsciously, to suit their personal and community aesthetics".
[4] In 2012, when
Bob Dylan was questioned over his alleged plagiarism of others music he responded, "It's an old thing – it's part of the tradition. It goes way back".
[5] Princeton University professor of American history
Sean Wilentz defended Dylan's appropriation of music stating "crediting bits and pieces of another's work is scholarly tradition, not an artistic tradition".
[6] In 1998, B.B. King stated on the issue, "I don't think anybody steals anything; all of us borrow."
[7]
}
Musical plagiarism - Wikipedia the free encyclopedia
It was just part of the genre.
So I come back to the board and as I turn the corner at a right angle I slip on the floor (probably a stray record cover) and go down splat. But I managed to raise my arm from the floor and hit the start button on TT2 for the segue just in time, and nobody in the audience noticed a thing.
I think there are a lot of blues songs that are really, really good. 
