Malcolm, I seem to recall that in the version you refer to above, the "earl" is the result of Debbie's misunderstanding of the pronunciation of "ale" - I think she learned the song aurally on a trip to Ireland. Her version was published in Come For To Sing magazine in Chicago, & I might well have done the transcription, as I did their music copying at the time.

It's published in Dominic Behan's book "Ireland Sings." And indeed the translation from the Gaelic is attributed to James Stephens.

I've also heard it sung by Frank Harte, who debunked the "feudal lord claiming his feudal right" theory, and attributed the story to the prevalence in Ireland particularly of older men marrying much younger women.