Well, this is a pretty perfect usecase for AI (although it's also easy to just get shapefiles from NE and do it yourself, obviously).

Interestingly all of UAE, Yemen and Saudi Arabia have significant discrepancies between the World Factbook and their shapefiles (in every case overestimating), probably all related to not having had a demarcated border in the Rub Al Khali.

A quick lazy calculation (including adding in Antartica) the countries totals came up ~2,000,000km2 short. I don't care enough to dive deeper, but if no one is claiming that land I'll happily take it.