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 Sarah Gavin M 1861 +/- 4 yrs in Athlone parish, Co. Westmeath, I found 1 rcd.
For John Duffy M ditto, ditto. This is a MATCH. The two likely married each other. A view of the detailed M rcd should confirm this. If so, the rcd may also show their parent's names and other info.
For John Duffy B ???? somewhere in Ireland with a father forenamed Eugene, I found 1 possible rcd in 1844, Co. Cavan. This is a tad on the young side. Cavan abuts Westmeath.
For Sara(h) Gavin B 1836 +/- 4 yrs somewhere in Ireland with a father forenamed Michael, I found 2 rcds: 1833 Tipperary, and 1836 Roscommon. Roscommon abuts Westmeath.
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.