PS. Richie, I've drawn up a table with the Roxburghe and Deming texts in parallel, marking the bits that appear in one and not the other or are significantly different between them. I can't post it here, but I'll e-mail it to you if it would be helpful.

Also, having done this, I realize that I was wrong in my interpretation of "And pled forth the paymount for to plough the whole sea" in Jeff Stockton's version. It looks much more likely to come from "And set sail for Plymouth, to plow the salt sea" in the Deming text than from the older broadside lines about the Bedford and Portsmouth.

On the other hand, Stockton's version doesn't all derive from the Deming / Forget-me-not Songster text. His stanza 5: "O pardon, sweet William, and spare me my life. / Let me go distressed if I can't be your wife. / For pardon sweet William is the worst of all men, /For the Heavens will reward you when I am dead and gone." contains details from stanza 17 of the older broadside that are not in the Deming version – although a line from the equivalent stanza in the Deming version, "Is this the bride's bed I expected to find", turns up (with "bright bed") in Stockton's stanza 4. So Stockton's version can't be traced just to the Deming text or to the older broadside text: it contains elements specific to each of them. I wonder how often this happens in the other oral versions – and also what it means for tracing how the song evolved.