See, the thing with Irish songs is that, one, a lot of the songs have been passed down orally. Actually, I don’t think O’Carolan’s songs were published during his lifetime (don’t quote me on that and correct me if I’m wrong).
Something you really have to keep in mind is that both versions–actually, all versions mentioned in the above posts are someone else’s arrangments. It’s what THEY thought was nice; what someone else thought worked. The phrase in question is not a drastic melody change all things considered, so really there is no right or wrong.
I do love this piece, I must say! When I play it I’ve arranged it my own way entirely; it’s more fun, I think.