Originally Posted by Ari

If you have a reservation that has a UA PNR (this includes UA flights, UA space and any travel booked by UA on other carriers including award travel) and the MP# is in the PNR then the itinerary will show up online-- the whole itinerary in most cases.

Otherwise, it will not. In the case of USAir, there is no UA space and not UA flights and it was not booked by UA (I surmise), so no UA PNR and no listing in my itineraries.