Martin, a belated thanks for your contribution here. I ought to have known that anything involving Grattan Flood would not be straightforward. I'd be grateful for any information you may have about the Kilmore Quay carollers and their repertoire.
From all I've read it sounds as if they would be great guests at the next Sheffield Festival of Village Carols.
It also looks as if the songbook of Luke Wadding, A Smale Garland..., would be worth some research, as it apparently contains a number of "lost tunes".