Lanefan
Victoria Rules
In this case "one continuous campaign" I suspect means more than for 40-odd years his players/PCs have mostly picked up the action this session at the point they left off last session, occasionally swapping out parties or story-lines but that's it.I'll add, although this game is marketed as one continuous campaign... I don't think it truly is, at least in the way you'd first assume. Although much of the world is set in "alternate history Earth," apparently he replaced South America with Hyborea from Conan, and Middle-Earth is can be reached by the sea. Plus Greyhawk, and even Menzoberranzan (from Forgotten Realms) exist in this world too.
You're conflating "campaign" with "setting", perhaps. The setting can be whatever he wants it to be including mash-ups based on all kinds of sources. Hell, my own setting has (faux- in all cases) ancient Greece, early-Renaissance Britain, a Roman Empire, Sumerians, and Aztecs/Mayans all bordering on the same Mediterranean-size sea; never mind a couple of homebrew Human cultures and some Elves, Dwarves and Hobbits.