My ancestors are of Irish origin and I've recently discovered more information on my surname "Costlow." My music was recently played on an Irish Podcast, which is recorded in the Irish language. The Podcast host gave me some information.
The current spelling in Ireland is "Costelloe." However, they do pronounce it "Cost-low" and it has also been pronounced 'Cos-TELL-oe' in other parts of the world. The original Irish language version of "Costelloe" is "O Coisdealbha." I've also seen "O Choisdealbha," so I'm not sure which is correct...yet.
Maybe I'll change my name back to its original version. Hmm.