David, if you are going to search for the definitive version of a folk song you're going to be eternally frustrated - there's no such thing. Folk songs exist in parallel versions because that's how they've evolved, you can't say that one version is any more "right" or authentic than another. One of the fascinations of folk songs is how many variants there can be.

It can be annoying when you hear a version of a song and can't find that version of it, but that's life. At least with the internet it's now much easier to look for a version than it used to be, and you can always ask on here. But not every version has been recorded, and not every recording is on the internet.

If you can't find the version that first attracted you, then remember as much of it as you can and piece together the rest from other versions. As often as not, that's what traditional singers did, and it's how many revival singers construct their songs. As long as you don't make false claims about its authenticity, that's fine in my book.