Completely agree with your 'pinch of salt' comment, Mike. Too much of this has gone on in the past. If there's any truth in it let's see the evidence.

Apologies to Ian and Dave. I didn't mean to be dismissive. It is as you say well researched and presented and I have to agree with your second point.

None of the ballads that are supposed to refer to a particular historic incident prior to 1700 get all the facts right. Probably because most of them were written well after that incident and are based on hearsay, so we should not be looking for full accuracy when looking for a ballad origin. All we really need is that enough of the facts fit that specific incident as opposed to any other known incident. So we can very rarely deal with precise matching details.
We also need to factor in bias, often political bias. The ballad writers are just as fallible as the book authors, if not moreso.