About 30 years ago Peter Parkhill was collecting in Australia among Turkish, Greek and other immigrants from the Balkan peninsula and found that their music was indeed changing, via processes defined here and elsewhere as "traditional", over periods of less than 60 years. With only a passing interest in the detail (and therefore a memory probably full of holes) I believe he was able to demonstrate the process as applied to rebetika and published on it.

There are several differences between Professor Child and Peter Parkhill and I may be quite wrong about the one I think relevant to this discussion, but I've always been under the impression that Child, as a Professor of English Literature, wasn't at all interested in the musical aspects of his material except insofar as it influenced the survival of the particular item; instead he was interested in demonstrating the notion that there was great literary value in material that came from well outside the cultural elites.

Again, my understanding is that, although it was an enormously influential pioneering work, it was really just a series of snapshots (earlier perhaps than various recordings we all love but otherwise with no intrinsic differences about the role of texts) that others were subsequently able to use to develop arguments about "tradition" generally, let alone "musical tradition" specifically.

Cheers, Rowan