I research the Irish Family History Foundation's database. It contains 12,800,000 surviving rcds for abt 70% of Irish counties. Rcds are increasingly sparse B4 1840, rare B4 1800. Cos. Donegal and Derry were recently added to the database.
Note 1 - Without a KNOWN county, the chance of an ancestor's rcds NOT being in this database is AT LEAST 30%.
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 Dan(iel) O'Kane B 1856 (exact), Co. Derry, with the father's forename unknown, I found 1 rcd: Garvagh RC parish. Father's forename was Hugh.
For Hugh O'Kane M 1846 +/- 10 yrs, Co. Derry, I found 5 rcds: 1842 Magilligan, 1844 Maghera, 1847 Long Tower, 1851 Kilrea, and 1856 Feeny RC parishes.
For Susan Hegarty M ditto, I found 0 rcds. This infers all the rcds for Hugh are likely false positives.
For Hugh O'Kane B 1805 +/- 5 yrs, Co. Derry, I found 0 rcds.
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.