"While Gamekeepers lie sleeping, a fragment of a song generally speaking, apart from the version Bob Roberts sings..."

I'll take on trust what you say about Bob Roberts embellishing the story, but Bob Copper knew seven verses of the song, which is a pretty large fragment. Anyway Bob Roberts didn't set himself up as the leading expert, didn't write a book, didn't publish his recreations, etc., etc., so there's no comparison with Bert.

"yet they forget that all songs were composed at some point and many trad songs have been altered by anonymous writers..."

The kind of people you were referring to so disparagingly know all of that very well.