Bryn, in the USA it picks up verses from "Lonesome Dove," "Blackest Crow," "My Dearest Dear," etc, to become "A-Rovin' on a Winter's Night."

I do think the song, as it exists in tradition, is a mass of floating verses, which Bruce disagrees with on the other thread. I will grant that it retains a core of the 1690 broadside in many cases. However, this is really just a matter of perception.   If you have enough verses from that broadside, you'll call it a version of "10,000 Miles," and if you have fewer verses from the broadside but more from elsewhere, you'll call it something else--maybe "The Blackest Crow." Songs exist in tradition with many verses from the broadside, and they exist with few verses from there. The point is that, like all lyric songs, this song-family is expressing emotion more than it is telling a story. Because of that, it can include any verse that expresses the same or related essential emotions. "I love you and I'll miss you" are pretty well covered in tradition, so it can include a wide variety of verses.

For my folklore courses at universities, I've put together a compilation of versions that I play for my class, slowly turning "My Dearest Dear" into Burns's "My Love is Like a Red Red Rose," even though the beginning and ending songs share no actual verses. I use it to demonstrate this quality of lyric folksong as a pool of verses to choose from, as well as a pool of "set songs." Ballads tend to be much more set, because of the need to tell a story.