Now, it seems, people are re-inventing dictionary definitions

There have not been any dictionary definitions, Jim. Only yours. The song I put up fits your definition to a tee. Is that so difficult to accept? Tell you what though, if you want a songs that have very similar melodic structure and timing to Nancy Mulligan though, try mixing Star of the County Down with bits of Byker Hill for a start. There are many more. Now, I have addressed every single one of your points and it is your turn. Explain to us how, by your own definition, Nancy Mulligan is not in the folk idiom.