> Pretty Polly still seems to me to be related in the theme of the lover who lures the woman away, meaning to murder her. <

Both those (families of) ballads have that theme, but I see minimal resemblance otherwise and many major differences, including the crucial difference that in one the girl is murdered and in the other she outwits the villain.

But anyway this was thread drift away from the listing of ballads missing from Child and discussion of why they are missing.

One, not mentioned so far, that seems to me a more deserving candidate than some of those that he did include is The Three Butchers, Roud 17. Printed versions go back to the 1600s and collected versions vary considerably in wording and tune, though with the plot remaining consistent. So it is certainly old and it was certainly popular.