I now have a specific reference to a document that ties the Nova Scotia Phinneys back to Barnstable.
There reportedly is an "Heirs Agreement" dated 17 July 1784 involving "Isaac Phinney of Granville in the ... province of Nova Scotia, the only surviving son of Thomas Phinney, late of Barnstable ..." The citation I have is Barnstable Probate, vol. 23, p. 443.
This presumably is in the probate file of Thomas, who died 10 June 1784, will dated 24 April 1780, proved 19 July 1784.
What's the easiest/quickest/cheapest/best (recognizing those are not always the same) way to get an actual copy of the Heirs Agreement? I'm in Arizona.