Hi - Actually this isn't a very specific use of a tally table for one customer.

This is called the "Retail Calendar" and is used by pretty much every retail business including the one I work for. We have retail stores and we have a large factory.

You can google it and look it up.

I don't know if this person is on the retail calendar or if he just has a weird fiscal set up.

I have been using a similar tally table for several years. One of the things I include is whether that particular date is a "working factory day". That doesn't mean to exclude sat/sun/holiday. As we approach the holidays we often have sat/sun where the factory works and ships product. So after the fact we add a Y if the factory worked that day.