As we all know, Bob did that with folks songs too - Scarboro Fair, Leaving Of Liverpool et al. In fact I heard his "farewell" song - can't remember the name of it - on a Judy Collins album long before I ever encountered Liverpool, which is/was more popular in the UK than the States.

Learning about the former didn't in any way decrease my love for the latter. I think in his artistry he managed to make the originals equal more than the sum of their parts.