Perhaps my comment was a bit too glib and simplistic. I don't think the folk idiom lends itself to much examination because there are too many outside influences at work when it comes to passing down songs from generation to generation unchanged. Someone learning a song that calls for an F major chord has small hands, so they play a 3 string Dm instead. No big deal in and of itself, but it changes the feel of the song.
Plus as you well know, blues people especially are fond of adding their favorite licks to anything they play. Hell, Frank and I are guilty of the same thing. (He's just much better than I am at doing it.)
Good case in point: I forgot the words to an old song Brownie McGee once showed me called "Livin' With The Blues". I remembered the chords. Mary Katherine Aldin sent me a copy of a the song on cassette. Sure enough, it was Brownie singing it with a band, but the chords were completely different!!
I remember Flatt and Scruggs hitting the stage with Earl feeling devilish, and he kicked off "Foggy Mountain Breakdown" so fast, most of the band couldn't keep up that night. Sounded like a 45 played at 78. Was it "untraditional"? Would purists hear it and say that's not the correct speed? If the guy that writes it doesn't play it the same way everytime, which is the "correct" version, worthy of preserving for all time for future generations?
Frank Hamilton does an interesting little chord turnaround on "Red Rosey Bush" that breathes new life into that song for me. His "Buffalo Skinners" has a dark undertone to it which I love, compared to Roger McGuinn's somewhat lighter version in his Folkden. Both Frank and Roger are skilled musicians, and they're gonna bring those skills into play on ANY song they choose to play.
Attempts to trace linage absolutely, or to freeze music at some point in time, are a pointless exercise, or so it seems to me, simply because the mists of time obscure our vision when we try to go too far back, and freeze drying, as we all know, loses much of the fresh flavor.