Jim
Don't know about you, but even with the advantage of having an accidentally acquired handwritten reference from Walker, I had great difficulty in tracing who I now believe to be the author of the song - god bless the internet - which MacColl did not have access to.
I find it interesting that MacColl's mistake has been taken up by others who have not researched the facts of the matter.
It has always struck me that folk song scholarship has, certainly up to comparatively recently, been a somewhat hit-and-miss affair outside the field of dedicated research - and even there, there are huge gaps in our knowledge due to misconceptions (don't get me started on why nobody ever bothered asking our field singers their opinions on their songs).
Jim Carroll