The CTO's may be lenient because this is specifically allowed. Unfortunately, when you combine vouchers with coupons, AA's computers don't know how to handle that, and so the agents have to do everything manually, including deducting the tax. (They call this "phase 4") The agents at the airports often don't know how to do this, and so they tell people that those things can't be combined, but the agents at the CTO know exactly what needs to be done. If you must do your ticketing at the airport and you don't want to wait for over an hour for someone to figure it out, call ahead of time and explain what you have, and ask them to do the phase 4 calculation. Then your airport agent can issue the ticket in less than 5 minutes.