Is your MP# in? Plug in your itinerary if it isn't showing in "my itineraries" and make sure your res is there with your MP# attached (and if you can't get it in, AS res can) and then see if you can WL from My Itins. The worst case is at the airport, if that segment is being credited to AS, you can WL. Your corp TA's system, if it properly has your AS and UA #s in there will properly link the segments to the proper mileage #s.