Dunno, PG. If the actors in your 'stage Irish' aren't being coached for authenticity, it's highly likely that they'll end up with slightly different Irish accents. I don't know much about accents, but I always notice that kind of thing ("oh, is he not from round here, then?"). As for singers, I always want to ask singers with fake American accents which part of the US they think they're from. I'm a great believer in making the song your own - which means not putting on any of the stereotypical 'folk voices', as far as possible, as well as not doing foreign accents.