Hamish Henderson considered Scotland and the north of Ireland to be a single area in terms of song circulation; so do I. You have only to consider the extent to which there were exchanges, from before the plantation of Ulster, in both directions, of people and traders across 'the narrow sea' - permanent migrants, seasonal migrants (tattie howkers), traveller families (Cathie Stewart was born in Strabane, Co Tyrone) and holiday makers - all of whom might have (and clearly did) carried songs. Paul, I can send you a paper I wrote (some time ago) giving details of some of the musical links between Scotland and Ulster). If you're interested, send an email address to jmoul81075@aol.com