Hi Daniel and Robin,
This is a small bit of information regarding your grandmother Sarah Callaghan.
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Sarah Callaghan was baptised on the 2nd of November 1886 in St Columbas Chapel (Massmount), Tamney, Fanad.
Sarah's parents were recorded as Daniel Callaghan (Murren) and Hannah Carr. God-parents were recorded as being Bernard Carr and Grace Carr, which would possibly a brother of Hannah Carrs from Ballylar, in north Fanad.
As regards to the Civil Registering of her Birth, Sarah was recorded as being born a month later, on the 06 December 1886 in the Parish Birth Registry for Clondavaddog (registered in the Town of Milford) - Parents Daniel Callaghan & Hannah Carr .
This was quite common at the time to have discrepancies conflicting birth dates, as a hefty fine would be imposed on the parents of a child if the birth was not registered within al least two weeks of the actual birth. The distance to Milford Town to register a birth would have been a full day’s trek on foot, with very few modes of transport been available at the time, it was just easier to bend and manipulate the dates to suit, and sure no one would be any the wiser.
Birth Cert - Irishgenealogy.ie (Cert also attached Below)
The Marriage of Sarahs parents was also registered in the Town Milford in 1886 : Daniel Callaghan and Hannah Carr Callaghan m02Feb1886, Fathers Michael Callaghan, Murren and Antoin Carr from Ballylar
Marriage Cert - Irishgenealogy.ie (Cert also attached below)