I am surprised at the way you were handled. I am a PM and have had three operational upgrades out of JFK trans-Atlantic this year, all on U fares, all an hour or more before boarding, simply based on the oversold situation in the back cabin. On one flight, my SM wife and non-status child were all moved to BE with me. Why? I think simply that the computer would allow it as an operational upgrade and thereby free up three coach seats for the oversell situation.
I have never been asked for certificates or for miles, although I have my certificates in my hand luggage at all times.