A follow up...
I called the Anual Passholder phone number and the CM told me not to worry, I can check-in and tell the desk I am purchasing a new AP the following day (I am arriving late night) and they will allow me to keep the AP room discount.
I also emailed the Passholder address... The response was very different, seemed more a corporate answer quoting the policy: "If you have booked a room with an Annual Passholder discount you will want to be sure to do the upgrade prior to the check-in for that particular trip. The policy is that you have a valid Annual Pass at the time of check in."
Oh well... back to square one.