We tend to forget that Britain was fighting France over North America at the same time it was fighting the newly named Americans. This map (from the Wikipedia article on French and Indian War) shows the status as of 1783. Pittsburgh and Colebrook, NH are right on that line between "always British" and "recently aquired by the British." If Scotch-Irish settlers were of use to the British authorities as the holders of the outlying settlements, those would be the places they'd settle. The American Revolutionary War battles over Quebec and Montreal went through Vermont and pretty much bypassed the areas noted in the list of ballad sources in NH. I can't speak for the Vermont sources. There were naval movements from the St. Lawrence and Lake Champlain, so certainly sailors could have been involved there.