William Snow was married at St Thomas the Apostle, Exeter in 1661 and 9 of his children (which was probably all of them) were baptised there.  The only event relating to anyone called Snow prior to 1661 at this church was the baptism of John Snow in 1590/1. Baptisms of William Snow between 1635 and 1643 occurred at Crediton, Atherington, Littleham by Bideford and Sandford. None of these is very close to Exeter so it was probably none of these.