Called Marriott number 1-800-535-4028 and inquired about the status challenges. The representative had to get help but after a brief hold was able to find the challenge to go from Gold to Platinum with 16 eligible nights. I asked about an existing booking and she indicated that only bookings made after the promotion was added will count (even if you haven't stayed yet). I asked about cancelling and rebooking and she indicated I could in fact cancel my booking and rebook the exact same thing to get those nights added.