For more on the historical basis of the ballad, and some interesting comments on how it may actually be more accurate in some respects than the official historical record, see David Buchan, 'History and Harlaw', in E B Lyle (ed), Ballad Studies, 1976, 29-40.

Buchan also speculates that Laing found (and published, but only in abbreviated form) a genuine survival of the original ballad and (as was his habit, though we don't know that it happened in this case) printed it on songsheets which then circulated through the region, giving rise to all subsequently recovered examples. Interesting, but circumstantial; and of course we have no way of telling whether or not there is any link with the song mentioned, but not quoted, in the 16th century. There are other possibilities: a poem on the subject appeared in Ramsay's The Evergreen in 1724, for instance, and Laing believed it to be considerably older.