Do you have any descendents for your 18th century PITHERs?
My gg grandmother was Sarah PITHER born in Crondall, Hampshire (UK) about 1838. She married Anthony Freeman in 1857. She had an older brother James, born in about 1830 and a sister Mary Ann born in about 1833. James married twice and had quite a few children. Their parents were James, born in about 1806 (probably in Crondall) and Sarah, born in about 1808. That James had a brother William born in about 1816 who married Martha, born about 1826.
Are any of these PITHERs connected? I wonder if the marriage of James PITHER and Sarah MERCER that you refer to is the one of my ggg grandparents.