I wouldn't try to put a lot of meaning into the Reilly refacimento which is obviously based on Child21 with bits of other songs thrown in as a chorus. I'm not suggesting necessarily that Reilly rewrote a version of Child 21 himself but that someone else did and it eventually came down to him. Travellers have often used ballads from books and it's remarkable how quickly they pass back into oral tradition. There are plenty of examples of this among the Scottish travellers.

The Maid and the Palmer has various analogues on the continent but The Cruel Mother doesn't.

I used to sing Child 21 to the basic tune of Tam Lin and it worked fine. Having said that, the Tam Lin tune I used probably came from Bert Lloyd anyway.