Just to be clear, I was making a joke about the persistent idea that every song (in the version we know) represents a True Story, which we can identify if we try hard enough. The way stories and their meanings shift as words get lost and replaced - the 'brother' line is a classic example - seems to be very hard for people to get to grips with. Trying to nail down the details of a traditional ballad to a specific historical event is very often quixotic if not daft, and trying to do this on the basis of a late version of a song is particularly daft. But it doesn't stop people trying!