Oh, it gets better. In the US in the finance industry there are days that are holidays for specific markets. So you need to separate out things like the stock and bond markets since they sometimes differ.

And just when you thought it was under control, consider what you do if the holiday falls on the weekend. Do you take it Monday or Friday? There is no consistent rule and so correcting holidays is a periodic maintainance headache that everyone has to do every so often...