When adapting traditional songs, there's often a fine dividing line between 'arrangement' and new work. I've reworked a lot of Child ballads and broadsides in my time, not only by collating different versions, but also by rewriting texts and inventing entirely new lines or even the odd stanza. I've also tweaked many a song melody. But all of that goes down as 'Trad., arr', unless I've written a new tune (which I've done in several cases particularly on the Peterloo broadsides), in which case it's 'Words trad., arr., music B Peters'.

I've never come across a version of 'Canadee-i-o' that looks much like Nic's, but there are quite a few out there. FWIW I do know his source for 'Ten Thousand Miles', and there he follows the Appalachian original quite closely, though the lengthening of some notes gives the rhythm a different feel, and then of course there's the guitar part. On the other hand I'm pretty sure he wrote tunes to broadsides which were credited as 'Trad., arr.' regardless. Whether the tune to Canadee-i-o is an old one or his own work, it's credited on the record as 'Trad., arr.', so someone else learning the song from Nic's version would not be obliged to credit him. However I have heard of instances in which an artist doing a cover version of someone else's 'Trad., arr.' song has voluntarily chosen to credit that person's arrangement if they've based the cover very closely on it. In the Nic's case, bearing in mind his enforced retirement, that might have been the moral high ground. And of course it's a matter of courtesy to credit your source for a traditional song, both in liner notes and live performance, as several people who've learned ballads from me have been good enough to do.