My wife always calls as soon as we are eligible for upgrades regardless of EUA and if they say that we must wait for EUA, she keeps trying each day until day of flight when it becomes a moot point and we just get to the airport early but it works for us. She usually (Silver) has a 66 to 75% success rate for overall upgrades and my Gold rate is even higher overall. If we get EUA, great but we never ever rely on it. Also if we don't get what we like from one agent, you can always try try again and again