Reminds my of Alan Lomax asking Muddy Waters about Muddy's sources on the "Plantation Recordings" CD.

Went something like this;

LOMAX: Did you write that song?

MUDDY: Yes, Sir, I did. I wrote it all by myself.

LOMAX: What kind of tuning is that anyway?

MUDDY: Span-cih

LOMAX: We're you learn that tuning?

MUDDY: I learnt it from Son House.

LOMAX: Did you hera Son House do that song?

MUDDY: Yes, sir, I did.

Like Alex says, in blues there are so many borrowed lines that just keep getting recycled into other folks songs. Many have no ownership.

Woke up this mornin'
Lookin' round for my shoes (X2)
Know by that, Lord
Got them walking blues

This verse was bouncing all around the blues scene in the 1920's, thought Robert Johnson is probably credited with it but Furray Lewis used it, Son House used it and probably a few others.

If the river was whiskey
I'd be a diving duck (X2)
I'd dive down to the bottom
and never come up

Furray Lewis, Muddy, etc

Engineer blew the whistle
Fireman rung the bell......
Credited to Son House but ya hear this line thrown into a few songs by contemporary blues artist...

Just a few examples. As a blues player, I have become less and less bogged down with personal credit and more appreciative of collective credit when it comes to these verses that were probably field hollers back on the plantations that were just passed from generation to generation.

Bobert