Happy Birthday, John L. Sullivan?

On October 15, 1858, John L. Sullivan was born in Boston's South End. 

Or was he?

John L. always gave his birthday as October 15. His mother and father did the same. Instead of a Bible, the Sullivan family recorded the birth dates of John L. and his siblings in the front of Life of the Blessed Virgin and Life of Christ. The date recorded inside is also October 15. 

Yet, the city of Boston birth certificate for John L. Sullivan lists his birth date as October 12, 1858, as you can see here. 

City records from the 1800s were susceptible to errors. Sullivan's death certificate, for instance, listed his incorrect age when he passed away. I would chalk the discrepancy up to a city error except for John L. Sullivan's baptismal record. According to the record I received from the Archdiocese of Boston, Sullivan was baptized on October 13, 1858, at St. Joseph's Church in Roxbury. Below is an older record of Sullivan's baptism:

So who's right? God, country, or the "Boston Strong Boy"? I think in this case, church and state have got it right. October 12 is Sullivan's birthday.