Dave has it right. All you need to do is sail one day during December to get double credits. That's why November 26 sailings qualify for the credit bonus. My Nov. 26 ends on Dec. 4th. It's a 8 night cruise so I'll get 16 credits. I'm staying on for the 6 night cruise sailing on the 4th for another 12 points, giving me a total of 28 points. I'll have a total of 538 points when I'm done. I needed 525 points to get my third amenity. I did B2B's during the December Diamond Celebration--I was happy to see they are doing it again this year. For some people getting to Diamond Plus status will be a lot quicker if they do the Diamond Celebration every year.