I always thought codesharing was meant for connections. Say I need to go from VIE to YOW. I can go to the OS ticket office and get an itinerary with OS flight numbers. OS71 to YYZ and then OS7337 or whatever from YYZ-YOW on AC metal. Most of the YOW/YUL flights from YYZ are codeshared on by UA, OS and LH.