But here's where that example points to another aspect of this kind of discussion. One of the criteria that gets repeatedly listed in order for a piece of music and/or a song to be traditional (folk) is that it has to be passed on aurally. In the case of paddymac's example, the song was being passed on in printed form ("as a printed street ballad").

So by the "aural tradition" of trad./folk music, a song doesn't qualify. Or so it seems to me.