Discworld runs on Rule Of Funny just as much as Roger Rabbit does, but the author was very good about continuity so there were rarely noticeable direct conflicts.
Agreed, that's what I mean! For a series that runs on "Rule of Funny" (or as Granny Weatherwax would put it, the "story") it's all surprisingly consistent. I'm not saying there aren't inconsistencies, but far fewer than one would expect from comedy literature.
You just made me realize that what made the latest Dungeons and Dragons movie so fun is that it cribbed a lot from Discworld. It has an irreverent sense of humor but never sacrifices the consistency of its world for a cheap joke.
I find the strongest differences are between early and later Pratchett, but there are big streaks of consistency across novels, especially within a "sub-series", e.g. all the Watch novels, all the Witches novels, all the "industry" novels, etc. Even they are often consistent across subseries.
That's why I think Discworld is surprisingly consistent, all things considered.
What don't you find internally consistent about Discworld?
Yes, it's full of gags and references to the modern world, but is that inconsistency? Or do you mean something else?