There are deadlines everywhere and there are individual employees who let them go sometimes. But, you can't count on it. Not on AA and not on any carrier.

This one is easy. At T-15, there's a WL. The agent clears the WL. This means off-loading the 5 and then issuing BP's and physically boarding the WL. Those people are now settled in as they ought to be.

Now, the 5 show up. The GA would have to physically (and in the system) off-load the WL, reissue the 5 who have just showed and then physically board them. This entails reopening the flight, retransmitting the data to dispatch to recalculate W&B (even though that won't change because the # of pax remains the same) and then hopefully getting all of this done for an ontime push.

None of this is meant to suggest that it can't be done. Simply to point out why it's a problem and why AA, along with other carriers, has rules.

You can always hope for an exception, but can't kvetch when you don't get it.