First, I totally agree that there are many mistakes in Jaquith & Walker. I was around, although not deeply involved, when they were putting the book together and it is a wonder there aren't more errors. They relied heavily on input from members of the family, and some of those folks had their own agendas. "Nuff said!"
It does seem to me that the 2 Josiahs are separated in the book. The one who married (1) Anna Holt and (2) Abigail ___, is my direct ancestor. As far as I know, he never left Windsor County. However, there is a book covering the history of Berkshire, VT and I have seen a photocopy in it of town documents listing both Josiah Sr. and Josiah Jr. I believe they are your Josiahs.
Anyway, good luck in straightening out the history.