Keep in mind that some Marriott properties overseas are franchise operations, and the credit card charge might have the name of the local hotel operator, not Marriott, Sheraton, etc. As a result, the system does not code properly as 6x, and the credit does not work. Happened to me in South America last year. The charge showed up as a third-party company that turned out to be the name of the franchise hotel operator. It took a call to Amex, and the rep said they could offer the points as a "one-time goodwill gesture." I guess I won't be staying at that property again.