Nigel, thanks for the head's up and your work on this.
When I was in Wales last month, I met with Rhidian Griffiths, retired from the National Library. We were talking about how some of these songs were written down. He said that often these songs were originally sung with instrumental accompanying, and that when the source sang for the collector, they would sing fa-la or whatever for the instrumental breaks. That makes sense. I never could understand why there was so much of the fa-laing in English music. It's more like the Irish lilting, I guess, where musical syllables were substituted when instruments were not available.
Thanks, Chris