Some of the "facts" are also matters where maybe there isn't a full consensus. The number of moons of Earth is one such example. It depends a great deal on how you even define the word "moon" -- I haven't checked QI's videos lately to see how, or if, they acknowledge this point, but I'm fairly sure that the answer changes each time it's brought up on the show, which sort of tells you that there's controversy. In that sense, the "fact" on the show is more about encouraging people to make sure they are better-read on a topic before proclaiming a given answer.