Canned Heat are hardly alone in not giving proper composing rights to songs. The Stones ripping off the Staple Singers for The Last time and Howling Wolf for Little Red Rooster, Andy's pal Robert Plant and Led Zep ripping off everyone etc. I wonder how much of that was down to management and record companies though since the Stones later gave a lot of help to Wolf and most of the white blues enthusiasts always went out of their way to name check their influences in any interviews they gave.

Also, the authorship of blues songs was often a cause of much dispute between blues musicians themselves. Did those songs all come out of Robert Johnson's head or did he hear at least some of them from an older unknown musician who never happened to cross the path of a pioneering recording engineer on a field trip ? Some of the most famous of the fifties Chicago bluesmen claimed writing credits on record for long established blues standards that originated in the delta. 

whs

Chuck Berry managed to get damages from the Beach Boys for ripping off Sweet Little Sixteen in Surfing USA. Can't remember if it went to court or if they settled beforehand. Now musically, Sweet Little Sixteen is a pretty basic twelve bar riff but at the same time the link with Surfing USA is immediately obvious. Muddy Waters and Bo Diddley also fell out over I'm a Man / Mannish Boy, where the only difference seemed to be in tempo. That never went to court though, probably sorted by the Chess brothers who they both recorded for.

Haven't got the Dylan album but if I remember correctly, the first verse was the usual "rollin' all night long" but then Dylan wrote umpteen subsequent verses that are indisputably his own. So another grey area there I guess. Not sure who to credit Rollin' and Tumblin' to anyway, it's normally given to Muddy but I think earlier versions can be found. I know a bit about early blues but won't claim expert status !