Query on Mary REYNOLDS

These 2 sisters have the same name and birth date but died 6 years apart.

Mary Reynolds born 19/3/1820 died 8/10/1866
Mary Jane Smith born 19/3/1820 died 28/9/1875

Father - James Reynolds
Mother - Martha Reynolds

Attached to Mary Jane Smith are several records
1) Death Certificate - Mary SMITH died 28/9/1875, father James REYNOLDS, mother Martha KILPACK, spouse William SMITH
2) Grave Record - Mary SMITH nee REYNOLDS born 19/3/1820 died 28/9/1875, wife of William SMITH

Can anyone provide any sources for the other Mary's death date of 8/10/1866