The register of the parish or surrounding parishes if the bride was from a neighbouring parish is the only place you can find that type of information at such early dates, particularly for RC folk.
Many people don't have death certs, they are not required for burial in Ireland as they are in some other countries so people just didn't bother registering the death as the cert was never needed for anything. Until the 1900s most people didn't own any land, farms were leased from landlords so apart from a few personal belongings there was nothing to inherit so no will was required, few families could afford headstones, graves were marked with a large stone or plant of some type and few churches kept burial registers so peoples deaths while marked by their loved ones at the time were never recorded on paper or stone unless a later generation put their names on a headstone but this depends on the later generation knowing the names of their great grandparents etc. and where they were buried.
