I think the problem has to do with them filming the school episodes first, and then filming the resort episodes next, and then filming the finale, and then the Hawaiian Style movie.
That was supposed to end the series.
But then NBC decided that they wanted to continue it, and would splice the school and resort episodes together instead of holding them over for the summer. Only, the actresses playing Jessie and Kelly didn’t want to return and since their contract was expired, they hired a new actress to play Tori for 1/2 of what would become the last season.
Only… instead of airing it the way it was ultimately aired, they’re doing it in production order, which is actually throwing everything off.