Note that the PMUs may expire before your status ends. If you are a recurring Platinum, your PMUs will be issued last thing (i.e. February) and will expire at the same time of your status. If you were a newly-minted in mid-year Platinum, your PMUs would have been issued mid-year when you reached Platinum and will expire before your status.

You can book advance flights and confirm upgrades outside of the PMU expiration date. However, you must turn in the certificate before the expiration date. You can do this at an airport check-in counter or Crown Room.