That is the problem with "the oral tradition". How can you certify the source? In the past, before music became a specatator sport, sharing music by learning it "orally" was the way music was shared.   Does that mean that because of recording devices, folk music has died? If you recorded Brasser Copper singing a song, gave me that tape, and I learned the song from Brasser's recording - would I still be part of the "oral tradition"? If Brasser heard Bing Crosby sing the song (far-fetched example perhaps) and it colored his version of it, would the song still be learned in the "oral tradition"?

Granted, some of the better collectors were able to trace and sort out all of these issues.   The point I have been trying to make is that the definition for "oral tradition" might need to change with the times, otherwise we can no longer trust ANY source singer born in the last 100 years.