I was too young by far to be one of the authentic folk revival characters, a decade younger than the Dylans and Baez's, 15 years younger than the Dave Van Ronks, or Rambling Jack Elliots, and PPM and the Kingston Trio were darn close to my mother in age. So I was never part of the experience of hearing a song circulate in some authentic culture that my grandparents or ethnics in my neighborhood belonged to and then bring it to Greenwich Village to enter the general stew being sung here and there until someone decided to pick it up and rework it to be performance ready. By the time a song reached me, it had been filtered through Peter, Paul, and Mary or the Kingston Trio. At best, I might have gotten it from Pete Seeger or Oscar Brand. Sometimes you wondered if the modern group had written it, but it was mostly understood that they had gotten it from Somewhere Authentic. The more commercial they were, the more they came in for disdain from the "real" folksingers. I understand that Dave Van Ronk was a particular bear for authenticity.
But the snobbery of it descended even unto me, and I willingly participated. If you knew something about the song before one of the commercial folksingers got it onto an album, you made sure you mentioned it. You wanted to show off by pushing it back as far as possible, deep into the hill country, or even better, back across the ocean to the British Isles. Whoa, baby, you were sumpin' then if you knew that the song was in the Childe Ballads in six versions and the reference to "the sea" meant in this case the Irish Sea, not the North Sea as was popularly supposed by other (ahem, ignorant) people. Because there was a coolness hierarchy, people would just make stuff up about it. If the song was sung by Hudie Ledbetter, then no one dared challenge you that it was based on southern black, and ultimately an African song. Because Leadbelly would know, right?
Well, know, he wouldn't really. He picked up songs wherever he went and sang them if he thought whatever audience he was playing for might like them and pay money for it. How we continually forget that these were people who were just scraping by, trying to make a living ultimately devalues their real lives. They weren't suburban kids trying to preserve some imagined cultural legacy, they were trying to eat. We project ourselves onto them.
Nonetheless, I believed an incredible amount of this crap that I had heard at coffee houses from performers who were good at patter when introducing a song. When I actually started researching a bunch of American songs for a US History paper in 11th grade I found that the stories were quite different. In particular, the earlier versions, if they carried political messages at all, didn't necessarily fit the Approved Coffee House beliefs. Roll of the dice there. Worse, I found that the information wasn't hard to find at the local library. The librarian over the record collection knew a lot of the info off the top of her head, actually, and could put her hands on the proper volume or record jacket instantly.
So you can do a really deep dive on both of these songs if you like, but I think a little will suffice, because as one should expect, there is no one single true version.Sometimes there's a trial, sometimes there isn't, sometimes the woman's testimony frees the man, sometimes condemns him. The usual.
One more thing. I will point back yet again to my post about the grim topics of folks songs. My children went to Christian schools that discouraged or even forbade listening to certain rock bands because of the terrible things said. I chuckled about this to my sons as I drove them to school listening to Steeleye Span and other folk songs about human sacrifice, rape and abandonment, kidnapping, maiming and torture, fratricide, and twenty versions of revenge.
Polly Von, Polly Vaughn, can be understood in terms of the Celtic for "Fair Mary" that sounds like Molly Bawn. (r's in the middle of first names often change to l's - see also Dorothy/Dolly, Sarah/Sally - and it was thought clever and humorous to nickname someone by changing the first letter, as in William/Billy, Robert/Bob/Hob/Nob) Not only the Irish had legends of women who could turn into swans and back again and were perilously fair to behold and supernaturally dangerous in some way. I had thought it sounded suspicious because swans don't taste good, so why shoot one, but I later learned that many people think they taste fine.
Folk song development note: I thought "He took her for a..." seemed a little ambiguous, as in most current English dialects "took her for..." would end with "a ride," or some such. So I switched it to "He mistook her for a swan" for clarity. I understood that others might prefer the sound of the PPM lyric. I also later learned that in British dialects "he took her..." still carried that meaning of "he saw her as..." But eventually I understood that this is exactly how folks songs change over time.
The Lily of the West is English, sometimes talking about an Irish woman. It's west of England, anyway. In the British Isles the woman's testimony was more likely to get him sprung. When it migrated to America the woman's testimony more often condemned him.