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 county, 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 Robert Coogan B 1868 +/- 4 yrs somewhere in Ireland with the father's forename unknown, I found 0 rcds.
For Ellen Brennan B 1873 ditto, I found 119 rcds. With a father forenamed Martin, there is just 1 rcd in 1872, Co. Kilkenny.
For Martin Brennan M 1868 +/- 4 yrs somewhere in Ireland, I found 40 rcds with 16 in Kilkenny. Of these, 3 are in Castlecomer CP: 2-1867, and 1868.
For Ellen Comfort M ditto, I found 8 rcds with 6 in Kilenny. Of these, 1 is in Castlecomer CP, but in 1870. This doesn't match with any of the rcds for Martin.
For Martin Brennan B 1845 +/- 4 yrs somewhere in Ireland with the father's forename unknown, I found 51 rcds, 23 in Kilkenny, 2 in Castlecomer RC parish. Both fathers were named John.
For Ellen Comfort B 1847 ditto, I found 20 rcds, 15 in Kilkenny, 1 in Castlecomer RC parish. Father's forename was Edward.
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.