otp means as you have guessed of this parish. So at the time they married Ann Burdett and John Bliss were living in Dunstable. bp is the standard abbreviation for baptised. I believe John Bowler and Ann had John Bliss 1783 -1852, Jesse 1785, Thomas 1787-88, Martha 1789 -1854, Ann 1792 (baptisms found and checked in Dunstable parish register) Robert Burdett 1796 -1862, Frances 1798, Joseph and Mary (twins) 1799 who appear to have been baptised twice - at Bath Abbey and Walcot, and finally Frederick Edward. I think John Bowler may have been baptised in Woburn which is not that far from Dunstable - there is a baptism there which could be him but I cannot prove it.