Here's what the American Express website has to say about this:
What if I cancel a prepaid hotel booking for which I received the $200 Hotel Credit?
When a booking is cancelled and a refund is issued that results in the purchase being less than $200 and you received the $200 Hotel Credit for the booking, the amount of that credit may be reversed. If the replacement booking is not made in the same calendar year as the original booking, the Hotel Credit available in the new calendar year will be applied to the replacement booking (if eligible).
https://www.americanexpress.com/en-u...-hotel-credit/