Harrington - Clashing baptism dates

Hi. I've progressed pretty well with my research into my Harrington ancestry in Cork. I initially traced my Great Grandfather, Daniel Harrington, by his Baptism record in Schull East (15/7/1853). I then established his parent were Patrick Harrington and Anne (Nancy/Anastasia) Downey and traced their marriage record of 2/9/1852 in Schull West (now Goleen). This eventually led me to Patrick's parents, John Harrington (my Great Great Great Grandfather) and Mary Mahony, who married on 12/2/1825 at Rossalettiri & Kilkeraunmore (Roscarbery & Lissevard). However, while I've identified the other children of John and Mary, there is a discrepancy which appears to tie in with the move from Rossalettiri & Kilkeraunmore and Schull, in that I have Baptism records to the same parents for a Norry Harrington on 2/1/1827 in Schull East, as well as for a Joan Harrington on 24/4/1827 at Rossalettiri & Kilkeraunmore.

I've checked for other potential John/Mary marriages in the area, but found none, so I'm keen to understand if there is any logical reason why either of the dates for the baptisms of Norry and Joan may not tie in directly with their births (I understood that baptisms usually took place within days of the birth).

I also know that Daniel migrated to England (his son Patrick, my Gradfather, was born in Stepney, East London on 1/3/1894). while I know that there were few, if any, immigration records between Ireland and the UK at this time, is there any other way of tracing their route and identifying when they moved? Daniel appears to be the eldest child, with

Regards,

Dave.