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Clonakilty RC baptismal records start in August 1809 so it is possible that Paul was born earlier than August 1809 which means no record. www.irishgenealogy.ie did show an 1817 baptismal record in the neighboring RC parish of Roscarbery but based on your note, it is likely too late. I lean towards a birth date before August 1809.
You may want to consider autosomal DNA testing.
Let me know if you have questions.
Area - CORK & ROSS (RC) , Parish/Church/Congregation - ROSSALETTIRI & KILKERAUNMOR (ROSCARBERY & LISSEVARD)
Baptism of PAUL SPILAIN of N/R on 10 June 1817
NamePAUL SPILAINDate of BirthN/R N/R N/RAddressN/RFatherDANL SPILAINMotherHELENA DONOVAN
Sponsor 1DANL SPILAIN