Reading these early Discworld, I've been trying to isolate the specific point at which a reader can see an embryonic Discworld transform into THE DISCWORLD.
It's in here somewhere. Sixth book of a series.
Trying to be specific; it might be the point at which the witches are trying to guide the troupe back to Lancre under the guise of harmless old crones collecting firewood.
It might be Nanny Ogg singing "The Hedgehog Can Never Be Buggered At All".
It might just be Nanny Ogg.
Either way, this is The Discworld.
Contains spoilers
I mostly kid. It's fine.