I hadn't heard "Nancy Mulligan" before, so I just followed that YouTube link.

I'm not fond of the arrangement (boringly stereotypical folk-rock beat), but the tune is in traditional Irish idiom and the lyrics tell much the same story as "Kisses Sweeter Than Wine", which is another folk-ish song that went feral in the pop world fifty years ago, and which some of the best-informed folkies the time certainly approved of. I can't imagine a situation where you could sing "Spancil Hill" but not "Nancy Mulligan".