Chris B, though you posted long ago, I am going to defend Christy Moore. On the Planxty album where his Musgrave first appeared, he wrote in the notes that he had always loved Musgrave but could not sing it until he found a Nic Jones album in Liam O'Flynn's flat with a goos tune! So he does credit that he took the tune from Jones. However, the planxty arrangement was quite different, with riffs and instrumental breaks and chord patterns nowhere to be found on Nic's version, so the arrangement could rightly be ascribed to Planxty (who at that time included not only Moore/Irvine/O'Flynn and Lunny, but also Bill Whelan of "Riverdance" fame, Matt Molloy of "Chieftains" fame, and a couple of others).

Whether Nic ever got any money from it, I don't know, but unlike Dylan's version of Canadee-i-o, it would have been a negligible royalty in any case! (I wonder if Christy ever made money on it!)The credit was the important thing, and it was publicly acknowledged by the band.