I've always treated the anniversary of Celtic Woman as September 15th, the day they recorded their first PBS special / DVD at the Helix in Dublin in 2004.
Celtic Woman Limited was set up after the DVD recording, on October 5th, 2004. Sources: [
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2]
But I was a little surprised today to hear a few times from Mairead Nesbitt that the actual Celtic Woman anniversary is June 9th. I knew they had recorded the album months prior to the DVD, but that far in advance, on the same day as the birthday of Chloë Agnew and David Downes? I haven't heard that before.
It seems odd that it wouldn't have come up more often. Maybe they celebrated it privately. Maybe they talked about it before I was on social media or forums.
So far, I haven't found evidence to confirm or deny that June 9th is when Celtic Woman actually started. Does anyone know?