I'm not going to tell you how many hours I have spent on this quest; only that the song is worth every minute.

Where I particularly hear two different tunes, is, speaking relevant to the text, the melody that goes with
"Tiocfaidh me 's ni fhanfaidh me,/Bi romham agus leanfad tu"
and
"Do cheath me mo bhroga leat,/Do ghearr síos na scorthai leat"
and
"Cead mile failte romhat,/Failte agus fiche romhat" (Mary O'Hara sings this verse, Maire Ni Scolai omits it)

That phrase has what I would describe (classical music theory betrays itself here) as a flatted seventh, in which the seven of the eight notes in the scale points downward to the note before it instead of being a "leading tone" to the tonic above it. NOT present in any of the "Robin Adair" melodies I have seen printed or heard played. To me it makes a great difference, but that's only me talking.

Translation? The more, the merrier. Many thanks, michaelr.