Thank you for the explanation. I may be doing something wrong, but it appears I am seeing something different. For instance, if you look at UA flight 862 SFO-DEN on May 6, you will see availability of NF1 NC0 on 757 equipment. But if you pull up the seat map either on KVS or on united.com you will see there are only two cabins (even though United.com does say there is both an F and C cabin, and you can click on seating for either F or C, but you will see that the seat rows are the same). The same shows on 319 equipment for UA flight 838 SFO-DFW May 6 (there are no UA 319's with 3 cabins- that I know of anyway!). Thanks again.
Its a documented fact that some of UA's 2 class aircraft also have NC/XC space, these most often have the same flight numbers as international 3 cabin flights, or are a continuation of an international flight
For example, UA862 is also HKG-SFO, UA838 comes from NRT, the SFO-DEN/DTW flights is on a 2 cabin aircraft, but carries C/F award space since its a "direct" international flight
There are a couple threads on this in the UA forum
So just because business class availability shows, this plane will NOT have business class.