I just did the "Live Chat" and asked about the nights. I was told the themed dining schedule has not yet been set for our cruise. She said the Pirate Night will be updated under "My Plans" once it is set, but that formal and semi-formal nights are not listed there. She also said that most 7 day cruises will have both formal and semi-formal nights, so I guess expect that.
So far, we've only done SWDAS cruises, which, I believe do not have a semi-formal night.
So, I guess the answer is "stay tuned". She thought that we'd know more in the new year.