It was my experience, upon leaping from Gold to Platinum, that any reservation I made while I was still a Gold but actually checked in as a Platinum, the system still reflected that I was a Gold, so it was a small process to get Platinum benefits at check in. Knowing what I know now, I'd call the hotels in advance to advise of my status so I'd have the best chance of a pre-upgrade or being slotted for a good room.