it's small wonder that Martin Carthy decided to look elsewhere

Quite. But it wasn't his idea to use the Breton pipe tune Son Ar Chistr for Willie's Lady. Ray Fisher had the original inspiration and Martin used it with permission.

And yes, Andy Irvine was indeed 'inspired' (or lucky) to have put the 'wrong' tune to WoW.

And you know how much I like your FF, Brian.