On the 1871 census a John S. Parr is living at Seadyke, Gedney with his grandparents a Richard Parr, 57, Ag. Lab., and his a wife Ann. He is the eldest of 4 grandchildren in the household. Also present are 2 unmarried daughters one of which is listed as Susan A. Parr, age 30 a Nurse, probably John's mother.
Looking back to the 1861 census the family were at 4 West End, Gedney, at that time there were 5 unmarried daughters at home, including a Susannah A. Parr 20 and one Grandchild.
The only registration of a birth for Susan Parr that I can attribute to John's mother is that for a Susan Ellis Parr, Holbeach, June 1840, 14, 389. I would say that the registrar misheard the name allocated and wrote Ellis instead of Alice. This child's mother's maiden name was ROWLET. I have looked at the births of some of her sisters and they also gave Rowlet as MMN. John Grandparents were probably Richard Parr and Ann Rowlet.