Recently, the agents at LAX have been very short on patience.
"Just cause you meal listed, doesn't mean you are listed for the flight. Please go to customer service and get put on the standby list. I don't have the time to do it for you!"
That was said to me week prior to X mas at LAX 55 min prior to departure time. I had already listed via ID90 and jump frequently. She wasn't the first to tell me this. The customer service center is hit or miss for a huge line. If you have the time, best to get there way early, go complete your ID90 listing at the CS desk, then at the gate your name will already be on the stby list.
Good luck!