Originally Posted by bwoodlandca

I have never used an upgrade certificate before. I booked a UAL domestic flight a few weeks ago. Yesterday I received a paper 1,000-mile one-way upgrade from the UAL Visa. I called United reservations, and they took about 30 minutes to finally apply the upgrade, he then told me I need to surrender the paper upgrade certificate at the airport on the day of travel. They also never asked me for the codes on the certificate, they either believed me on my word, or somehow looked up this certificate of mine while they were on the phone with me? I checked online a few minutes later, and the upgrade did go through: it showed my First class seats and said “Upgrade confirmed”. So here is my question: Can they change my seat back to economy on the day of travel when I check-in if:
I forget to bring the certificate?
They do not ask for it when I check in? Can they later deduct miles from my account? Can I use it again if they do not ask for it.
They notice an error by the reservations agent in booking the upgrade? I am concerned because the certificate said I needed to pay Y or B (full fares) to use the upgrade, but my original ticket was W (discounted). Also, the certificate is for a 1,000 mile upgrade, but my first leg is 900 miles, and the second leg (on another flight) is 400 miles, yet they put me in first class for both of those flights, which are over 1,000 miles.
Can I check-in online if I am supposed to surrender the certificate? If so, who would collect the certificate if I go directly to the gate on the day of travel?