Michael,
We are discussing the probable origins of the corpus collected in England and published by the likes of Sharp in the early 20th century. I have spent many years studying multiple versions of oral and printed ballads and have arrived at the conclusion that the vast majority of them actually originated either in the theatres and pleasure gardens in the towns, or were produced by the hacks that lived near the printers in the towns. In 89% of the corpus under consideration the earliest surviving example is from sheet music or street literature. Based on the comparative study of many versions and those we definitely know to have originated in this way I arrive at my conclusions. As Jim quite rightly states, I can't prove this beyond all reasonable doubt just as he or you can't prove they were made up by country people in rural settings.