It seems to me that "The Douglas Tragedy" was crafted out of Earl Bran. All variants of Child #7 in which the name Earl Bran is used have no motif. That's 7 out of 10. The 3 that have it of course use the name Douglas. Interestingly, these versions use the rose and briar but then switch to the second part of the variation (aye they grew etc.)This doesn't happen anywhere else. The Douglas is an example of a ballad that was tailored to fit the legend and a locale. No big mystery here. We can scratch this one off I think.

I like what Mrs. Laidlaw said. It's folk wisdom for the ages. Publishing ballads is like reducing a motion picture to a still. But I also respect your analysis Michael. It's brilliant. I've got some good stuff to ponder out in the woods where I'm a-going right now :)