Couple of points - I downgraded within the 30 day window, but haven't received the 85K cert yet - the Marriott Amex cert arrives a couple of months after the card anniversary date. But the Amex rep assured me, and data points indicate, that you earn the annual night based on what card you hold on your anniversary date - the card you have when the cert hits your account doesn't matter. I will let the thread know when I actually receive my cert. And you are right, you would have to reupgrade before the anniversary date if you want to receive the 85K cert. However, I am not sure if Amex would consider that gaming, so personally I am planning to reupgrade only if I need the status.

Also note that the 25 elite night benefit also appears to be just based on holding the card for any point in time of the year - new applicants get the 25 nights immediately, and they don't claw back nights if you downgrade or cancel. Also important for those that had 52 elite nights at the end of 2022; they "earn" Platinum with the help of the 25 elite nights, so if you downgrade or cancel, you keep that Platinum status and the 25 elite nights in 2023.