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The subscription site Roots Ireland shows that Catherine was baptized on January 1, 1893 which would reinforce the Charistmas 1892 birth date. Parents were given 30 days to report to the local Registrar and register a birth. Many times because of weather, distance to the town, etc. the 30 days would pass. I believe there was a fine beyond 30 days so many times parents just adjusted the birth date to stay within the 30 day window for registration.
FYI. The offical birth record is the record you viewed on www.irishgenealogy.ie
Name:Catherine SullivanDate of Birth:
Date of Baptism:01-Jan-1893Address:KilanninParish/District:MOYCULLENGender:FemaleCountyCo. Galway
Father:Redmond SullivanMother:Mary ConnorOccupation:
Sponsor 1 /
Informant 1:Martin Connor Sponsor 2 /
Informant 2:Bridget Connor