Apparently "America's Next Top Model: All-Stars" is actually just the seventeenth season of the show. They just changed name (or, added to the name) and changed the premise a bit (not adding to the cast).
I wonder what fueled the decision though. Did they really think they they'd just run out of all the drama ladened, aspiring fashion models out there? If a quarter of the people who have sex on camera and end up on the Internet, want to be models, then that show would never run out of contestants.
Actually though, "America's Next Top Model: Porn-Stars" would be a much better show, I'd love to see whatever drama those girls have!