Part of his great talent was that of weaving together factual minutiae with fictional minutiae such that the boundaries are impossible to spot without prior knowledge!

Even if you know you have to keep your eye open for it. E.g. my personal favourite is that I 100% did not spot until it was pointed out to me that the printing dwarfs in The Truth are all named after fonts...

The Annotated Pratchett File lists many similar references Pratchett included in his novels. In this case, it's marked as p35 of Reaper Man:

https://www.lspace.org/books/apf/reaper-man.html