Shakespeare is in fact a very good example, he was a playwright, not a historian of any kind. But he did draw on the work of historians including Raphael Hollinshead. Hollinshead's work in some places offended the Privy Council who removed some places, but Hollinshead's work still exists in its entirety. Shakespeare did exactly what the songwriters did, which is to take history, embelish it, and superimpose a bias which is either theirs or the bias of those who pay them. Shakespeare's history is folk history.

Modern historians would not dream of taking Shakespeare into account without understanding this, and looking for corroboration of anything they might find. So it is with folk songs.

Jim says of a song he posted:

"This song quite possibly depicts an actual happening; if it does, the characters are unknown.
What it does do is describe a common occurrence in Irish rural life - and far beyond"

None of this is corroborated, and the first sentence can't be. The second might be, but I am not aware of documentary sources which would provide such corroboration.