There is a phenomena that has happened to me several times in my life, where one person copies something from another and then finds out that the first person did not make up it up after all.
Example: I misremembered the rainbow line from Sunshine Superman to include the line: "while I tie up rainbows you can have for your own" as if the guy were tying them in a bow for the girl on her velvet throne. I then used the idea of tying rainbows in a bow in my Prospero novel. It is one of the outlandish things Astreus Stormwind, the elf, offers to Miranda at Santa Claus's House.
So, my question is: who gets the credit for the idea? Can't be me, I borrowed it. It isn't the guy who wrote the song, his song doesn't actually say that. The Muses, maybe?