I've seen some posts the other-way i.e. UA SWUs on CO but not CO issued ones on UA. I'm thinking of booking a spring trip to ICN and I actually see R availability on UA 891. I can say this, I do have a half UA metal itinerary already (BOS-MCO on CO, then MCO-BOS on UA) and it WOULD NOT allow me to upgrade it at least online. So before I even consider booking this I would want to make sure I can in-fact use a CO issued SWU on that route. Thanks for your help!