I had a NW coded AS flight once SFO-SEA. I tried to call beforehand and similarly had no luck.

I tracked the flight with LmOffice by Luiz Miranda as well as with the FC seatmap on AS website. On the night before the flight, there were two seats open.

I got to SFO about 2-3 hrs before the flight and the check-in agent swiftly upgraded me to F.