Yeah what Stallionsden said. So, when you add prefabs like that, you're adding it to the world generation mixer. When you generate a new world (not just making a new game on Navezgane or Pregens), those prefabs will be added to the world if they can be. When you hit New Game on, say, Pregen01, that world was already created so the newly added prefabs won't be there. You can, however, use the World Editor to manually place those POIs inside of it, then start a New Game on that world. You can bypass adding POIs to an existing world, but you'll need to do a region reset or start a quest there for it to repopulate (although this is not a supported way, it just happens to sometimes work, although it can break things, so I suggest a new world to be safe).