Not to muddy the waters, but the relationship between broadsides and the oral tradition has to be considered. A theme or plot common to a tradition (or a number of traditions) may be reintroduced by a commericially printed 'original' composition. This 'new' ballad may be re-absorbed into the oral tradition. At what point does it become 'traditional'? I can't answer that question, but I think it is worth discussing.