As others have already pointed out BSC Child 65 has actually no text in common with Lady Maisry other than the commonplace little boy who runs an errand which is present in many ballads. It has its own intro with no mention of being pregnant and the burning episode has significant differences. BSC, only collected by Motherwell, was found only in the Glasgow area. The likelihood is that it is a late ballad based loosely on the plot of Lady Maisry. It's not beyond Motherwell's own pen despite the fact that he claimed to collect several versions.

Significantly Child makes no mention of BSC in his headnotes.

As for JJN, well..... I think that's been adequately dealt with elsewhere.