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).
Note 4 - Microfilms of parish church rcds are kept by the National Library of Ireland.
For John McGrotty B 1870 +/- 4 yrs, somewhere in Ireland, with the father's forename unknown, I found 3 rcds: 2-1869 Derry, 1-church (Limavady RC), 1-civil (Limavady RD), and 1-civil rcd, 1871 Derry (Coleraine RD). Father's respective forenames were Edward, Edward, and James.
For Pat(rick) McGrotty B 1879 ditto, I found 2 rcds: both 1878, Co. Derry, 1-civil (Glendermot RD), 1-church (Waterside RC). Father's forenames were both James.
Since the B rcds for the two appear in different parishes/districts, there is a big question whether the two persons were related. You will need exact DOB, parent(s) name(s), and/or placename(s) to pick which, if any, rcds are for these ancestors.
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.
Hope this helps. Good luck.