And the upgrade request (using the E cert) can be made within the SE upgrade window. I know, because I had (according to the computer) become a SE in early 2004, but my SE package did not arrive until later in Feb of last year. I still had many E certs, so I continued to use them - no trouble at all from the AC check-in or gate agents. However (I am speculating now), you may experience some difficulties, if you check in at a foreign airport, and the agent checking in for AC flights is an employee of another airline.