I have sat at a bar listening to Maggie Barry singing "The Galway Shawl" and in another pub I have heard Luke Kelly belting out "The Oul' Triangle".   I have heard these songs about a thousand times each. I've even been known to sing them. Not once did it occur to me that they have the same tune. I gather from the reactions of Brían above that I am not the only one. You live and, sometimes, you learn.