Originally Posted by
Flying Machine
.... Amex requires a same day boarding pass departing from the airport of the lounge that you're visiting....
This may be true when a lounge is crowded, but it is not the published policy:
Access to The Centurion Lounge is complimentary for global Platinum Card® and Centurion® Members. To access The Centurion Lounge, the Card Member must present The Centurion Lounge agent with the following upon each visit: his or her valid Card, a boarding pass showing a confirmed reservation for same-day travel on any carrier and a government-issued I.D- name on card must match government-issued I.D.
Note: The Centurion Lounge is a Day of Departure lounge requiring confirmed travel plans. Passengers holding standby tickets and non-revenue standby passengers, including airline or industry employees traveling on discounted tickets, are not eligible to utilize the lounge unless they have received a boarding pass showing a confirmed seat or zone assignment for the flight for which they are on standby.