I'm not sure what Carthy's gripe was - neither song belonged to him anyway

It was - I believe - the arrangement that Paul Simon took. And the myth is that eventually (long after) Paul Simon gave Carthy 5,000 GBPs. I think there must have been a hole in his pocket and his trousers had turn-ups! There has been discussion in this parish on the subject.

And I do remember that the "hit" that Paul Simon had was "Scarborough Fair: Canticle", which allowed Simon to claim songwriting copyright or at least as "arrangement" (hence the royalties thereof) and in the latter case Carthy would have a beef.

And FWIW the Arlo Guthrie version of "City of New Orleans" was definitve, IMNSHO Johnny Cash would not have made quite such an iconic version. And I have heard tell that it took 6 months of re-arranging the song before Arlo was happy with the result. And the tme was well spent.