In a sense, my work here is done. The original post that started this thread, describes my dilemma then: a studio recording introduced me to this song. The mezzo-soprano singing "Eibhlín a Rúin" was Máire Ní Scolaí, and the vinyl 78 RPM single was recorded and issued by HMV just before the Second World War. I was struck by the combination -- a pleasant combination for a classically trained pianist/accompanist like myself -- of the traditional song, with its fluid rhythms, highly ornamented melody, and Gaelic lyrics, with an interpretation on voice and piano by two musicians who were obviously not traditional musicians in any sense but two concert artists bringing a traditional art form to the concert platform and recording studio. My dilemma was that the lyrics which I could find in print, for the most part did not at all match what Ní Scolaí was clearly singing. What were those lyrics, and where was the text preserved?

I also wondered where the melody, with its orientation toward modes rather than diatonic/leading-tone classical scales, was preserved.

That this thread has posed these questions for all to consider, is half the battle. Posts on this thread demonstrate some disagreements as to how to answer the questions, and there is nothing wrong with that. I am not completely satisfied with the results of the searches I have made myself, and will probably keep my unanswered question in the back of my mind, to recall on occasion.