Lighter wrote: But suppose I'd learned it from a live performance, determined the correct lyrics from a book, and taught it to somebody else twenty years later with minor changes.

In my book, your version would not be traditional. The version of the person who learned it from you might well be, though. If they'd just absorbed it from you, rather than you saying, "Here, learn this!"

On another topic, an analogy might be useful here,

Around 1905, Albert Einstein published Special Relativity, Brownian Motion, and the Photoelectic Effect. All major advances (although most people think someone else would have developed Special Relativity within five years if Einstein hadn't). In 1916, Einstein published General Relativity, and that was really, truly, and totally new.

In 1927, Werner Heisenberg announced the Uncertainty Principle, and Einstein couldn't take it. He tried so hard to prove it wrong that he fudged his math, then ceased to be a physicist and became an actor pretending to be a physicist. You can argue that he did good in that period (although it was also the period when he was hitting on his second wife's daughter while apparently abandoning his own daughter) -- but he wasn't a physicist, except in his own mind. He couldn't follow the field, because he no longer accepted what was happening.

Of course one can ignore new discoveries in any field. But one can't do it and still contribute to the field. It has moved on. I doubt any of us is an Einstein, but we can still learn from his mistake.