it is bizarre trying to upgrade any more on codeshares. Last Feb. flying TPA/YYZ/ORD/TPA. TPA/YYZ flying AC, ticketed AC, was allowed to upgrade for $55 (about the same price as certificates). YYZ/ORD/TPA, ticketed UA, flying AC to ORD then UA to tpa, could do nothing with UA certs in YYZ, had to run to the gate at ORD, and to add insult to injury, guess which segment I haven't gotten credit for yet---YYZ/ORD!