Formal night schedules on longer cruises seem never to be what you expect. At least that's my experience.
On one trip we expected three, had two. On another, we expected three, had four.
It's pretty much up to the onboard staff, I understand. It's easy for the guys -- just send your shirt to the laundry. It's tougher for the ladies. This is where the ever-serviceable LBD (Little Black Dress) comes in. Of course, there are the on-board boutiques if you get caught short.
pamda -- CM First-Time Cruisers Editor and aficionada of the LBD
On the past May transatlantic on the Galaxy there were three formal nights (I am 99.99% sure). As cruising goes it was a fairly traditional cruise in that people abided by the dress code. And it was a fantastic cruise.