Premex:
It's never happened to me on United, but I saw it happen to 4 other pax a couple weeks ago on a ORD-OAK 757. After we were all on and boarding was completed the gate agent went back and got 4 pax out of coach and moved them up to first. I assume they had been on the wait list.
I watched this wondering if the upgrades were freebies. Certainly appeared so, as the agent seated the pax, turned and headed for the door. Just shy of the door she stopped and suddenly returned. She realized she had forgotten to collect the upgrade coupons

Nope, no freebie tonight ... she stood there and waited while each of the pax dug for their coupons.
Robert Johnson
danville 1K