I've been finding this discussion of a song I'm very interested in really useful - thanks all. Though trying to follow the thread on a phone on the other side of the world doesn't make it easy to analyse everything as thoroughly as I'd like. I was looking at 'Pretty Polly' from the point of view of Cecil Sharp's Appalachian collection, so was effectively working backwards from the North American versions. I was interested in three features that occur in the texts of most of those:

'Leaving the small birds to weep and to mourn' - retained from the old 'Gosport Tragedy', but not in any of the British 'Polly's Love'-type broadsides, or oral texts.

'A spade standing by' - not in 'Gosport', but unlikely to have been an American interpolation as it's present in nearly all the 'Polly's Love' BSs in England. Jim Brown has now tracked it back to 1801 in Scotland (though of course it might go back further than that). Thanks, Jim.

'You guessed about right' (or similar) - replacing 'he said that is true' in v16 of GT. This seems to be present in many of the US and Nova Scotia texts (though not all), but I've never seen it in a print copy apart from the Forget-me-not / Deming / Baltimore example discussed here. So can we say that is definitely an American addition?

Quite apart from that is the question of how and when the older ballad got shortened to the three-line stanza familiar from bluegrass repertoire. Any ideas, Richie? From what I can remember of Sharp's Appalachian versions there were examples of both types coexisting in the mountains, with some in the old triple-time and some in 4:4.

And then there's the question of how the ballad got to the mountains in the first place: oral tradition amongst British migrants, early American broadside (maybe picked up in Philadelphia by migrants), or a bit of both?