IIRC, I first heard of "Lord" Franklin in the influential version sung by the late Mícheál Ó Domhnaill of the Bothy Band in the early '80s. A. L. Lloyd recorded the song around 1957. I don't think he called Franklin "Lord."

But since he called the song "Lady Franklin's Lament," the change to "Lord" is perfectly understandable.

More than you want to know: http://stessily.hubpages.com/hub/Mchel-Domhnaill-Kevin-Burke-and-Lord-Franklin-I-dreamed-a-dream-and-I-thought-it-true