I'd be interested to know for certain what the policy is on this one right now. The website says the coupon expires upon reaching Concierge, and the Concierge line told me quite confidently that the Platinum upgraded had been removed when I hit Concierge, but there seem to be a few people around here who've had the opposite experience.

Does anyone have any recent experience (ie this year) actually using an old Plat upgrade after reaching Concierge? Might be useful to the OP