OP, terrific story. Glad it worked out and thanks for sharing it with us. Persistence pays off indeed.
In summary:
- UA bean counters figured they could oversell C and downgrade an upgrader if necessary.
I think this has always been SOP with PMUA. It's not surprising that you were the lone upgrader on a Saturday transpac flight. I'd say Saturday is the most difficult day of the week for upgrading going in that direction.