If you want an upper bound, 163 countries and 2 territories have Christmas as a public holiday.

There’s going to be foreign nationals, people who don’t crare for their government etc. who are carveouts for independence days but your upper bound considers everyone in those countries - my issue is that your lower bounds are both very much lower bounds, but then you’ve got one upper bound which is an approximation which may be higher or lower than the total and another which is actually a upper bound seemingly just to get the conclusion you wanted