Your Sim version will always be up to date no matter what. Because you can’t fly the sim without the latest update.
World Update, is a completely separate thing. It’s like a DLC. You get this by claiming the free content from the Marketplace, and you download this through the content manager. So even if you download the Japan update, it just adds it to your collection of sceneries, airports, update packs. It doesn’t change your sim’s version at all.
Further updates will apply too. If there’s a World Update 4 in the future (wherever that is) your sim will get updated to that new version. But you will still don’t have the World Update yet, you have to do this step separately after updating the sim, claim the World Update 4, and it will download the content separately after that.