In the absence of hard evidence I can't see us getting beyond informed guesswork for most songs, based on subjective assessments of their wording.

If someone went to the considerable effort making all the texts computer readable then modern techniques of text analysis would probably help go beyond the subjective.

Even usage of individual words may tell us something. How often so words like 'lucubrate' and 'viands' (from The Sandman's last post) appear. Is that typical of the vocabulary of "somebody educated in a hedge school" ? (or am I missing some irony in that post)