I first had those verses years (no: decades) ago from Packie Manus Byrne, before this song became a favourite on the folk scene. (I think it was made popular, or at least helped along hugely, after Mary Black recorded it with De Danann, which brought it to the attention to a lot of folks.) I would say he is the source from which John M and Jo F got them (though I haven't asked them) because I know he had these words well before then.

It would not surprise me at all if he had written them because he has a gift for verse (and for blarney!), though the Woody Guthrie info above is new to me. Packie is not a particular Guthrie fan and doesn't follow his work, so it would be interesting to see WG's exact words and compare the two sets. But the verses above are pretty much word for word what Packie gave me back in the late 70s or early 80s.