Not Davy Graham's arrangement, Martin Carthy's.
I think there is a big difference between making up a new song, and making a new variant of a pre-existing song, and on the basis of that claiming some ownership of the song on which you built that variant.
But that's a side issue here. I'm looking forward to seeing that article if you can get it, rich. I noticed that the versions Parks collected came from as far apart as North Carolina and Texas, which indicates that it was widely dispersed, so I'd be surprised if no one collected versions from elsewhere, assuming that there were collectors looking in the right places.