Question Does the developer create their own game world using the modding kit released by them?

Like Mount & Blade Warband (modding kit) The Elder Scrolls (creation kit) Fallout(creation kit)

the developer also release the modding kit for each player,So I want to know do they create the main game world(do not include bottom technology like graphics/AI/ etc) also using the modding kit software or same software like parent of the release version just without great interface?

In my opinion the modding kit is like a world creator so they should also using this to create the world.

sorry for my English.

 

Bethesda has mentioned that they develop their games with the tools they release to the public.

 

The Modding SDK they deliver are mostly stripped down version of the more powerful tools they use in the company itself. not exclusively tho

 

Kind of along the same lines, I've seen some indie games made with Unity implement mods or "world creators" by having the modder actually install Unity, with the finished mod actually in the form on an Asset Bundle. I actually only first heard about this because we occasionally get a forum thread from a modder who gets stuck.