Jeff, thanks for that detail.
I forgot to also mention that the Lufthansa agent at LHR, for the LHR-CGN flight, also refused to reprint the boarding pass to put Aeroplan on it. I was able to get the SEA United agent to print the boarding passes for SEA-ORD and ORD-LHR with the Aeroplan #, but of course at LHR you have to check in again.