There are two records for Mary's baptism, identical in all respects except the date of the ceremony.

Durham Records Online
Baptisms, Sunderland District - Record Number: 708683.0
Location: Monkwearmouth
Church: St. Peter
Denomination: Anglican
24 Aug 1823 Mary Spain, of Monkwearmouth Shore, born 29-Jul 1823, daughter of William (mariner) & Margaret Spain

Baptisms, Sunderland District - Record Number: 708664.0
Location: Monkwearmouth
Church: St. Peter
Denomination: Anglican
30 Jul 1823 Mary Spain, of Monkwearmouth Shore, born 29-Jul 1823, daughter of William (mariner) & Margaret Spain.