"I think that the definition of a ballad as a song with an explicit narrative is a useful one - if you wish to split out specific classes of ballads (broadside, popular, modern, cowboy, whatever) that's what adjectives are for."

Err ... yes. I was trying to say that in my first post of 28th last month. You can't compare "ballads" such as "Tamlin" and "Leader of the Pack" because all they have in common is the narrative element. The cultural differences are too great - apples and oranges. If you can't compare them then you can't give them a common definition. What you can do is define categories of narrative song. This might involve the time periods in which they were composed; technical features such as rhyme and verse structure; geographical areas of composition; and (referencing WLD's post of 16th) the expectations of performer, audience, and professional agent.