dont u depart from Tom Bradley International Terminal

In any case, if you dont check-in an hour or more before an international flight, the airline can and sometimes will, deny your boarding. While NW told you the wrong terminal could have caused you to arrive to check-in counter too late, you were also cutting in too close. I would never arrive check-in counter less than 1.5 hour on an international flight, knowing the horrible security line to go thru and there is usually one flight per day to many not so frequently travelled destinations.

FYI, Qantas has TWO security check points to go thru - one is the U.S. airport security check point, and then Qantas has its own security check point and they screen your luggages one more time on their own machines.

I believe there are time limit posted either on LAX airport website, or on each airline own website.

I know AA can deny boarding even on domestic flight if you dont check-in 30 minutes before at any airport or 45 minutes at LAX & MIA, FWIW.