Am I correct inassuming that these songs can be dated from evidence from contemporary sources ie such a song was written by what's his name beacause people remeber hm doing it? And that songs have cultural clues which place them at a partcular time?

Both these strategies work to some extent with old songs (say 16C - 19C).

What struck me when reading Broadside Ballads from the Bodleian Collection is how manneredand artfully constructed many ballads seem to be when compared with the more straightforward style of songs collected from men and women a hundred odd years ago.