Originally Posted by YYZC2

Each container can hold 30-35 bags. 146 pax maximum, some with only hand carry, some with two big bags for an overseas trip... tough to say unless I have the numbers in front of me but a five-container bag load on an A320 is considered heavy.

I'm not going to speculate on what happened in this case but I will say it's possible to have containers go walkabout upon arrival as cargo, terminating baggage and connection baggage all get whisked away planeside by different vehicles. The containers are pretty generic, identified only on the manifest by their container number so it's easy for someone to grab the wrong one and take a bag can to cargo or vice versa. This issue may not be an LAX error but a YUL one.

I will dismiss the notion of someone at LAX "forgetting" to load the bags. Load instructions are scrupulously followed by ground crews and flight crews alike, so an aircraft departing without planned containers is almost impossible. If those containers were left behind in LA, it would have been with the full knowledge of the captain.