My outbound process was fairly simple as UA found F space. My return was different. TG changed equipment at my flight time and moved the 747 with F to earlier time. UA would not honor or grab me space on that flight hence the change for NRT. Spending evening in Tokyo at a lux hotel does it for me. There was never any explanation offered but me having e-mail confirmations and being able to quote directly from them helped make my case to stick with my original cabins. The prospect to visit the Royal Spa before departing BKK for NRT helped incentivize me to hold while they worked it out. I also offered to speak with the service director my GS agent was conversing with. Thanks all for encouragement. Suspect this will not be the last story we hear.
