Nether Update Not On World

The Nether update items and mobs work on all of my normal worlds. The problem is every world that I have bought off the marketplace just hasn't updated yet. None of the items mobs textures or mechanics are working or available. Even when I make a new world it just doesn't work. I have tried uninstalling and then reinstalling Minecraft, but it never fixed anything. I believe this may be a bug or it could be a problem with the world creators. Please fix, it would really help out in my roleplay worlds.