I fly monthly YUL to US, mostly on UA, and I get maybe once in 10 or 15 times the annoying "can't give you a boarding pass" on OLCI. The main issue with that is that the counter (and the kiosks) shuts off 60 mins before departure, so if you don't get there on time you're out - while with a printed boarding pass nobody cares as long as you make it to the gate before departure. Sounds like a small issue, but at 5am it's not... I don't know what the CO rules are - we'll see.