Last night, I booked a trip LAX-IAD-AMS, outbound on UA 966, connecting to UA 946. I am traveling with a friend on an award ticket so selected flights with both XC and NC availability.

When I went to apply my SWU to the outbound, UA 946 cleared immediately, yet UA 966 went to the waitlist.

I checked online and UA 966 is NF0 but NC 3.

What is the distinction between upgraded first and upgraded business on a two-class flight? How can I get me one of those NC seats?