Wait a minute, I already used a Warp Zone in my file. I was planning on just starting from World 1-1 on that file and going through the game to unlock World 9. But if I already used a Warp Zone and saved on that file, does that make it impossible to unlock World 9? I just want to make sure so I don't go through all that and see that I can't do it anymore.
Also, I heard that it's possible to lose World 9 after you unlock it. Is this true?