I don't know where I picked up some tidbits about the evolution process, but I read long ago that sometimes a new tack runs into a dead end, and if you don't preserve the old, you can't back up and start over. Martin Parker worked up a version of the farmer who changed places with his wife (see early version and "Wife of Auchtermuchty" on my website), but it was pretty terrible, and a dead end. Fortunately, older versions were still known, and it was reworked to the "Father Grumble" we have now. I like traditional to mean just that, and regard it as the process whereby the folk sort out the wheat from the chaff. That seems to have worked pretty well.