What's in a name?

So yesterday was March 17th - St. Patrick's Day, right? Well, no actually - it's a religious festival, and as such subject to the rules of the Church (Catholic Church, that is). And the rules do not allow St.Patrick's Day to be held during Holy Week - that is, the week leading up to Easter, i.e. this week. So.... it had to be moved for this year, and the Church decreed that it be observed on the 15th. So if you left it until yesterday, you were too late!