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The Booking Classes shown in Availability displays are indicative of the cabin configuration, i.e. if C/D/Z (Regular) or XC/NC (Award/Upgrade) Booking Classes are shown for a particular flight, then that flight does have a C cabin.
Using your example above, if you see NCx (including NC0), then it's a 3-cabin flight. A 2-cabin flight would have XF/NF/XY/NY. A 1-cabin flight would only show XY/NY.
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.