Pretty sure there are not 250 countries. How hard is it to validate the enormous number in the header image?

There is no correct answer for the number of countries in the world. I'd recommend this Map Men video on the difficulty of deciding what is or isn't a country: https://www.youtube.com/watch?v=3nB688xBYdY

There are some databases including territories and stuff that sometimes lands in the ~250 region, but should be stated if so. Closer to 200-210 or UNs "193 countries" tend to be a bit more common to use though, always depend on what exactly you see as a "country" I suppose.

There are 249 country codes, which is a possible definition used.