I probably keep my two cents out of this because the Pollys Bob was talking about are branched off from my Briggs line about three or four generations back. I am no expert in genealogy. If I were to pursue one of the Pollys Bob refered to it would be the daughter of Peter. Peter and his mother, Dameris, wife of James, are both buried in Akley Cemetery near Guilford, Windham Co., VT. I show (no documentation) Polly, daughter of Isaac, married to Noah Stockwell, September 29, 1807 in Athol, MA.She was also nine years younger than the Polly, daughter of Peter.
Bob has given you two strong leads. I use his information to help reinforce what I have listed on a regular basis.
To answer your other question about simular names in the families, Peter and Isaac had a sister named Mary,an uncle named George, a neice named Sally and Isaac had a daughter named Sally.
If you can establish that one of the Pollys is your Polly, Bob can take you back a few more generations.