The flight back was uneventful, which is what I like. I could not get a window seat, they were all taken by the time I arrived. However, I did get a "windowless window" seat! This is a seat against the side of the plane, but where there is no window. I think these used to be emergency exits, but British Airways decided they didn't need them, and that they could get more passengers on by removing them and replacing them with seats. I really would have liked a window seat, because the plane flies north west from London, following along Britain, then across Iceland and/or Greenland, Hudson's Bay and into Montana before reaching Seattle. At one time I got up to go the toilet, and out the window I could icebergs - which must have been huge, given we were at 35,000 feet! Later I saw what I thought was a big mountain, so I presume this was Greenland/Iceland. It was also a daylight flight, so there would have been no trouble seeing things. At least the plane was not full, and I had an empty seat next to me all the way.
I had no real troubles getting through Immigration at Seatac. The letter from the Embassy did the right thing. I was shunted off to the special processing area at the end, where they made the necessary checks before letting me in. They even gave the needed forms to apply for a replacement green card!