i dont get it

they obviously wrote and filmed it in a different order n figured that this episode would be a better ending to the season than the one they originally wrote for it. They've done it before with season 6 where cox shaved his head but then had hair again for an episode after, some shows get jiggled around and when its a comedy n quite a well loved goofy one, nobody really minds the time line being out as long as they get a giggle at the end of it. Face it its not a drama or a huge continuing story like lost, these things will happen.