one possible explanation of same date 'christening' is that the record is of reception into the congregation (or as would be used in a Roman Catholic church a conditional baptism if status of any prior baptism is unknown) - maybe a Quaker background may explain any doubt
You see similar 'double' baptisms in Manx records - one being a private baptism and 2nd is reception (normally both baptism + reception are done in the same ceremony)