Regarding the tune, it's notable that most performers sing certain, significant "wrong" notes, i.e. if we are in the key of C, they are singing the note A in 2 places they should be singing B. In no way am I suggesting there is only one "right" way to do things -- rather, just noting that the one authentic source for the song, Doerflinger's transcription of Maitland, is one way, whereas some early revivalist (Dubliners or whoever) changed it to the way nearly everyone does now. In sum: not much relevance from an artistic standpoint since art is as art does, but relevant if one is exploring "origins," where one needs to carefully check the primary source!