I research the Irish Family History Foundation's database. It contains 12,000,000 surviving rcds for abt 65% of Irish counties. Rcds are increasingly sparse B4 1840, rare B4 1800.
Note 1 - Without a KNOWN parish, the chance of an ancestor's rcds NOT being in this database is AT LEAST 35%.
Note 2 - Only 1/2 of Co. Cork's rcds are in this database.
Note 3 - The RC church kept control over most parish rcds from Tipperary (north). These are ONLY available thru the Tipperary Family History Research center at a substantial fee (regardless of outcome).
For Miles O'Reilly B 1818 +/- 1 yr somewhere in Ireland with the father's forename unknown, I found 2 rcds: 1817 WIK and 1819 CAV.
For Julia O'Reilly B 1827 +/- 2 yrs ditto, I found 5 B rcds: 1825 CRK, 1827 DUB, 1827 CRK, 1829 MEA, & 1829 WIK.
The 1819 rcd for Miles (CAV) and the 1827 rcd for Julia (DUB) have fathers forenamed Patrick. Patrick is so common that this occurrence could be pure coincidence.
Google the Foundation's name to lead you to this database. Register, opt to be notified as rcds are added and browse. Pls post your search results to my genforum msg.