Alan,
At least you've one acceptable date - the marriage in 1770 was extracted from the Bishop's transcript for that year
I dare say you've found the 104 entries for Mary B's in the IGI but your query doesn't mention the 1747 birth entry for a Little Barrington M. B.
However, the Eastleach Martin and the Little Barrington data are submitted entries giving no verifiable source information (BT's: PR's etc) so might be fairytales in one or two or all respects
The LDS formulae often used for "guessing" birth dates are marriage date minus 21 for females and minus 25 for males but they not a hard and fast rules.
You mention a birth in c1752 - the IGI does not give it and as it's circa 1752 it should not be accepted unless the source from which it comes is a verifiable church record.
Are you sure that their last child was actually born in 1797? It would be far from unusual for a baptism of a prospective bride or groom to be performed shortly before marriage.
The LDS library catalogue gives details of the filme of the BT's and registers for Little Barrington and it would be most unlikely the the register will help you. Perhaps the Gloster R.O. will have the Banns records which might - just might - help.
Regards
Chas
