Are you sure you were looking at the correct flight? -- UA.com is also showing NC1:
Maybe I am not understanding how building a fare works. I see NC=1 for ORD-BKK as you indicated. However, when I begin the trip by adding on a DAY-ORD segment, the NC space for ORD-BKK becomes zero.
Do the fare buckets change depending on the rest of the segments in that trip?