Tuesday is the beach party. Wednesday is repeaters and Lobster night. Repeaters dinner was being done outdoors in December. Friday is the Gala. Managers cocktail party was is on Thursday. If you've stayed at couples before, you should be invited to the repeaters dinner. You may want to ask about it when you check in just to be sure.
Just FYI all this information is listed under the "Special Nights at Couples San Souci" header in the Restaurants and Bars tab.