This is the winning statement right here. Just spent the last hour running around in circles with the standard Marriott reservations folks at the phone number on the back of the RC card. No one (3 reps) seemed to know how to attach the certificates, and they ended up booking me a rate that did not include the upgrade. One call to the number above (which is the standard RC reservations line) and they knew exactly what to do and modified the reservation. Luckily the hotel I was trying to book had the eligible rate available at no extra cost, and they just attached the certificates. But wow, was this frustrating. Save yourself some time and just call RC reservations directly when trying to use club level upgrade certs.