Maid of Australia and Brigg Fair do both have the air of being made by individuals who were there (in the former case, the location almost certainly being the Hawkesbury River in Australia, not anywhere in England, though the name got changed to "Oxborough" when the song came to England). The encounters recounted could very well have happened exactly as described or they could be fantasies.

Banks of Sweet Primroses is an oddity. It is very stable in both text and tune across many collected versions, clearly showing how much the folk liked it; and yet, as Steve Roud points out in the notes in The New Penguin Book of English Folk Songs "something of a mystery, as it always seems as if we do not have the full story. What has the man done to receive such an extreme and seemingly final rejection... ?"

And just who is saying what? It is presumably the girl who says "I'll go down ... where no man on earth shall e'er me find", but why make that declaration just then, after the encounter described in the song, rather than going down soon after whatever dirty deed the man did to her? And is it the male narrator who cheers himself up with the thought of a "sunshiny day"? (BTW, in my personal experience of weather in the London area it's more common for a sunshiny morning to be followed by overcast for the rest of the day.)

As I think I said somewhere up thread, it's easy to cite specific songs that were almost certainly written by "folk" in the countryside and others that were almost certainly written for the stage, the pleasure gardens, or directly for printing. The bone of contention is only the relative proportions among the collected corpus.