Michael, you are right about the origins of "She Moved Through the Fair". I guess what I meant was (what we all mean, really) is that it had been recieved into the *perceived* realm of trad.
Hold on, this gets into physics (and metaphysics): nothing has a reality of its own, but only exists as observed, right?
So I'll bring in another example, which was a "stealth" composed song for decades: Abdul el Bulbul Amir (and all variants). Long considered a "college song," it has finally been blamed on Percy French.
Which brings up a collateral question: whcih tradition(s) is/are considered truly "traditional"? The student song tradition was a healthy one from the Middle Ages until recorded music came in. Lord knows whether the once-prolific "skiing song" tradition is still going. These were, in fact, vibrant traditions, where no one asked who wrote the things they sang. They just learned them from each other and sang them. Frequently with gusto, and even more frequently with beer.
But I don't know that I could get away with offering a "traditional" set that included "Bulldog on the Bank" and some odes to schussing.
Whattaya think?