Joan says in her autobiography And A Voice To Sing With that during The Rolling Thunder Revue tour in 1975/76 Bob used to ask her to "sing the one about me" and she used to tease him with "you mean the one about David" [her husband], so there is a little bit of an excuse for people being confused.

And A Voice To Sing With (written about 20 years back) is a great read. It is out of print, but you can still pick up good copies second hand.

There is another song we've not mentioned yet she wrote about Bob too, which is For Bobby.