I'm afraid Grattan Flood is widely regarded in Ireland as something of a disaster for the history of traditional music. As for where the tunes came from in the first place, some historians would argue that moany, if not most, of the jigs and reels now associated with Ireland migrated there from Scotland.

And quite a number are thought to be of fairly recent origin - "composed" within the last 200 years or so. Even tunes written in living memory are quickly assimilated into the tradition, and assumed to be anon. Some of the leading instrumentalists seem to think it is almost obligatory to contribute an original tune to the repertoire, and many of these are soon forgotten. Some however - eg Junior Crehan - have written tunes that will live on for generations to come. Such tunes will be assumed to be traditional, and some latter-day Grattan Flood will pontificate on whether they came originally from Scotland or Ireland, or Brittany.....