I believe conventional wisdom is to link UA/CO accounts and use your UA status when flying UA and CO status when flying CO. Say that a United 1K, matched to CO Platinum, is flying a mixed itinerary, UA metal on the outbound and CO metal on the return though... what to do? UA status to upgrade the outbound, but then... do you switch to CO number after the upgrade clears on the outbound? or do you leave your existing 1K number in the reservation as the basis for clearing on the return trip? What's the collective wisdom on strategy here? Thanks!