In follow up I've double-checked the book.Strangely there were no marriages listed in the years 1784 or 1785.Surrounding years have an average of 4-5 marriages noted.
No ALGAR/ALGER baptized between Nov. 21, 1756 (Anne, dau. of John & Lydia ALGAR) & June 29, 1761 (William, son of Samuel & Mary ALGAR)... with the exception of a 4-year-old ALGAR born out of wedlock (baptized April 7, 1758).
Sadly, no Ann Salmon baptised between 1763-1765 either.
Perhaps your ALGAR/ALGERs belonged to a dissenting church & are not included in the OPR; I've found mention of several Baptist groups in the Diss area, Quakers too I believe.