I've come across one of the quirks in UA's system that I couldn't get satisfactorily answered by the reservation agents or a forum search.

My wife and I are travelling on UA917 IAD-SEA on July 30 on the same PNR. The flight, according to united.com and the phone agent, is showing NF1 and NC2, and is operated by a 2-cabin 757. We're waitlisted for the upgrade (the itinerary shows we're waitlisted for NF).

Based on some threads I found here, it seems either NC or NF could be used to clear this upgrade, but according to the phone agents, it is only NF. I understand that they sell this as a 3-class flight due to the flight number continuation from FRA, but it seems to defy conventional logic that NC > NF. If we wern't cleared/listed for NC, then who would be?