Do I detect a little naievity here? Most of the 'big ballads' are timeless STORIES. Even if there was an incident that inspired a particular reworking of the theme, it's almost always heavily vested in a mythological coating.

Just as an instance: since Lord Whatever killed both Matty/ Musgrave and the lady, who recorded the conversation between them about hearing the horn of Mattygrave's pal: "away, Musgrave, away"?

It's a timeless tragedy, a work of art, not a historical record.