They’re very different from the rest so it makes sense. IMO you’ve really got 4 eras: The first two, the era where he’s got an idea of what he wants but it’s still forming and being explored (pre industrial, lots of new stuff, characters change a lot as he explores them), his stride (longer series, less satirical, beginning to display his feelings on people as a whole), and then the embuggerance books (frustrated and powerful stories that leave very little of himself held back). They definitely bleed into each other, but there’s a reason Snuff feels a lot more like I Shall Wear Midnight in tone than it does to Guards Guards.

I think what he’s really saying is “don’t start with the books that came with an assumption that this was a one off parody, start where it’s being written as a series meant to evolve, then when you have a feel for it go read them”