In "On The Run", Amethyst's hole is behind her in this scene, as she and Steven were just inside of it before Pearl showed up. Now, remember the name of that one episode that hasn't aired yet? "The Kindergarten Kid"? It's possible that there's another Amethyst, and the episode "Steven vs. Amethyst" isn't even about our Amethyst.
This theory at least proves that there's one more gem like Amethyst out there, corrupted or not.