I think that Mssrs. McGrath and Offer are right in their opinions, as usually.
The problem of the source, on the contrary, is always that you only can get a reference or first record handwritten or printed. This naturally can say nothing about the real place and time of origin. Especially interesting is the wandering of the songs over boundaries - how come? Interesting question.
The story behind a song is the most interesting approach. E.g. when hearing a German masons' song about the dangers upon a scaffold I instantly was reminded of the hard working times of my youth, when I erected scaffolds most carefully, and how insecure I felt on top of them albeit.
Often songs describing historical events, now obscure, initialized me to do some some research, if only to know what people felt at those remoted times. And lo! there seldom is a difference to our times.
All in all, Torctgyd's question is a really good one in my opinion.
(Referring to McDonald may I remind you of another one, the farmer whose song I learned at school some 50 years ago?)