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 in 1864.
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. Roscommon is the more likely of the two. This MAY be for your ancestor - no guarantee. Hopefully a view of the detailed rcd will show the same parent names as were on the M rcd.
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.