That marriage date looks very odd to me.I was at the Dighton Library just the other day and got a copy of Briggs birth record transcripts (such as they are) from 1700-1899.According to them, Matthew Briggs and Mary (Pitts) had the following children:
Eliakim b.1733 Sept 21 Silvester b. 1735 Feb 5 Marcy b. 1739 Feb 3 Abigail b. 1742 Aug 10 Diadame b. 1744/5 July 20 Matthew b. 1747/8 Jan 16 Mary b. 1752 March 31
I didn't think to make a copy of Briggs marriage records--sorry!