My sisters and I have found two gravestones, both apparently for Matthew Card and his wife Susan Gardner West. The information on both stones is exactly the same, except the birth date for Matthew on the stone in Bristol, RI is October 11, 1817, while on the stone in the graveyard on Shermantown Road in North Kingston, RI, his birth date is shown as October 11, 1818. His death date and Susan's birth and death dates are identical on both stones.

Are these the same people, and if so, why do they have two stones?