Interesting Thread!
We were also booked in a First booking to New York. My partner is Gold and I was Silver (but Gold now!). They were able to book 1A (and K was free). I had to go in 2A.
Ironically, I had enough bookings 'pending' to show I would be Gold by the time we took the flight. But on the Gold Line BA would still not move me to 1K! This is sort of the opposite to when you drop to Silver and they boot you out. What about when you are Silver and you will be Gold at the time of the flight!? Ha Ha. Interesting.
Anyhow, someone took 1K in the meantime, so in the end we (and for other reasons than this) cancelled the entire Booking in the end. But an interesting Slant on it, and to be fair what can BA do but apply the rules......