I had a UA award that included a leg ICN-ORD in OZ F.
Did not ticket (OZ segment) the first time, so I had to call UA to fix it.
Checked the itinerary last week, and the segment was moved from Sat to Sun and from first to business. (the last segment ORD-STL was still on Sat)
I ended up finding availability the long way on LX in F.