When we cruised on the 4-night back in January. We had the PTTA rotation, so we repeated the same restaurants back to back. Pirate night was the same day that we were in CC, which was also the same night that we would have done Triton's for the 2nd time. There was a special pirate themed menu in the restaurants that night. Hope I didn't confuse you on this too much.
As far as the question about formal night on the 4-night cruise, you will probably get a lot of different answers to this. When we cruised, yes, the navigator did state that one of the nights was themed "dress-up" night. This was by no means a formal night, but the Navigator stated that the suggested attire was semi formal. Again, this came straight from my Navigator.
I hope this helps for you. If you have any other questions, please ask away!