Well - not exactly, both ships alternate between two different itineraries, Eastern and Western caribbean, each going a different direction each week.
It is the same two itineraries for both ships, but they do it like that for two reasons:
1. if you want the eastern or western caribbean you can go any week you want, you just pick one ship or the other (they will be nearly identical).
2. If you want to stay on either ship for two weeks you do not repeat the same itinerary, you get a 14-day cruise with all different ports.
See - there is some logic to what they do - they didn't just start doing this yesterday