Saint Declan, and Earc and Dubhthach, are The Dagda. A greatly loved Gaelic God, he's a patron of magic, paternity, fertility, life & death, seasons, airs & wind, and the sky itself. Whoa.
A god deeply meshed in the hinted-at Gaelic cosmogony, The Dagda as "Dáire" seems to arrange or kindle the coalescing Cosmic Person deity, Lugaid. Perhaps for this and other reasons, all three Saints share a mytheme of being the first supporter and sponsor of Patrick ("Saint Lugh") in their reluctant assemblies.
Today's issue is (belatedly) for "Saint Declan", but must include other names, too: Earc, Dubhthach, Fergus, and Eochaid.
I lack wordcount here, but I believe that Oghma's likely role as the God of Bardcraft was transferred to The Dagda, so that it's the latter who expresses godly musical power. "Fergus" of the Fianna is a Bard, and various Saints are associated with Bards and Poets. I suspect The Dagda had an underlying Triplicity, of which Oghma was part.