My take flight certificate conditions were misleading. One rule said it was good only on USAirways and USAirways Express flights. (Which could imply no codeshares). Another rule said codeshares were allowed. I booked a ticket on a codeshare flight operated by United over the phone. The person on the phone told me that was not allowed. I read the rules over the phone to her, she asked her supervisor and then they said yes I could use it and ticketed the flight for me. I guess anything is possible.