Led zeppelin took credit for songs that they didnt actually write. The greatest example of them all is whole lotta love which is a rip off of 'you need loving ' a song by a quite popular band of that time named smile faces check
even their most popular song ''stairway to heaven'' seems to come from another song called ''Taurus''
can you hear it?
There are many more songs that are taken from other artists and no credit was given to them. So saying that led zeppelin is the greatest cover band ever maybe isnt an overstatement.