Nick Dow makes a good point about tunes and their travels.

Another good thing to consider would be to go to the Roud Index and see how many of these various texts are found in broadsides. Broadsides were of course sold without tunes, and the sellers would often use a tune they knew. And so a tune that originated with one text would come to be associated with some other text. This happened a lot. Using Bronson's hints and that fact, you might even be able to figure out which songs are more likely to be "sources" and which "recipients."