> Misty Mountains of Home being a variant of Oh, Dear, What Can the Matter Be?

Never thought of that one, but it seems to be too true.

I don't suppose one can usefully talk about tunes that are secretly "the same" or "different" without specific qualification, but in my own mind they're different if the untutored listener (me) doesn't think, "Hey, that sounds almost exactly like ...!"

That means modal and minor versions of major tunes (and each other) are almost always "different" tunes.

The tune to "Sam Hall" currently sung is not the one that used to be popular. That was closer to the old tune(s) of "Captain Kidd."

Bertrand Bronson wrote a famous article on "Sam Hall" 's family tree in the 1940's.

Another relative is the hymn "Wondrous Love," though I don't think many people would say it was "the same" as any of the others. (Its tune used to be identified in the early nineteenth century as "Captain Kidd," leaving us to draw our own conclusions. I think it's the most powerful of all.)