Interesting post from Paul. It's difficult to guess how regionality works with tunes, I idly assumed that publishing them would freeze them a bit while an aural tradition would develop versions. I can quote examples to support and refute this assumption.

An example of a tune gaining regionality would be 'The Buff Coat Hath No Fellow' in Playford (can't remember which one so no date), tracked to the Lake District in (I think) the late 18th century, where it's a more lively jig and retitled 'She Wants A Fellow'. Greg might narrow down the date for me, but a hundred or so years and it's changed considerably.

Conversely, 'Le Nouvelle Fantasie', published by John Simpson (circa.1800) remains pretty much unchanged all over England and even when we find it in NSW, Australia (by Sally Sloane) in the 1950s, 150 years later, it's nearly note for note. No 'added value' as it were.

I think there are three states for tunes.

Tailor made (and hence serving the needs in the region of origin).
Adopted (unchanged because they have a use or a resonance)
Adopted and Adapted (Loads of tunes in that category these days).

Does the same apply to songs?