"221 - 406 of the book under discussion for meticulously researched evidence of the state of folk song in England from the 16th to the 19th century."
I've read this Vic - if you re-read it. Roud treats it as an Urban phenomenon and from the point of view of a town-based commercial enterprise
The songs he discusses are largely ones that did not pass into the singing tradition we are discussing here, but were created for town and city customers, full of Phillidas and Valentines rather the the folk's "Jimmys and Marys".
Charles Dibden was typical - a British composer, musician, dramatist, novelist and actor, with over 600 songs to his name who was nioted for his sea-songs but would probably have become seasick if he drank a glass of water

The traditional repertoire being discussed here is that of sailors, soldiers, land labourers and workers in rural industries such as textile work and mining - songs made by them and not about them.
There are snippets in passings about country singing in Roud and elsewhere, but by an large the songs have been regarded out of context, rather like butterfly collecting - objects in themselves rather than a part of the singers' lives - a social phenomena.

This argument has led me to revisit, Maud Karpeles's 'Cecil Sharp's Collection of English Folk Songs', and some of the contemporary collections
The thing that strikes me is how remarkably free they are of the stiltedly ham-fisted technique associated with the broadside hacks - not completely, but the ones that aren't stick out like so few sore thumbs.

It seems to me obvious that, rather than the folk taking from print, the opposite was the case - the hacks were borrowing ideas from sailors, embarking soldiers, countrymen coming to town to sell their produce and taking songs with dirt under their fingernails and turning them into the pap they ended up as on the presses.

We know country people made songs - we know the songs reflected fairly accurately country life and conditions - no 'sons of the soil' or jolly Jack tars' but real ploughboys, sea labourers and soldiers in the ranks - the voice of the people that they have always been regarded - up to recently (and by a few desk-jockeys).

A true approach to where our folk songs came from would be to gather together what contemporary information there is, including Baring Gould's writings, Sharps' diaries - anything else available - and compare it to the spurious (in my opinion) claims of literary origin and see which holds the most water - earliest publication dates mean nothing
I've often wondered if the BBC project recorded anything more than the songs - it would have been an ideal opportunity to gather information

We know that some of the motifs and references used in traditional song making go back to Shakespeare and Boccaccio, even as far as Homer, who was liberally borrowing from folk beliefs
Jim Carroll