I was looking at UA983 (HGH->SFO) on 9/26, the business class seats showing wide open (R9), but after I added another segment SFO->IAD to the same itinerary, the same HGH->SFO flight changed to R0. I am really puzzled

. Does anyone know why? Can I still call them to upgrade the HGH->SFO leg if i book the HGH->SFO->IAD flight?