You just had to post this, 19 days before I'm going on a flight...

I do think, however, that your thought of two flights, same day, same flight number, different times was likely the correct presumption. Especially if it was a fairly short hop flight. Which, especially with the recommendations of "arrive two hours before your flight, yada yada yada," makes it easy for someone to arrive early, breeze through security, hear their flight number, and try to board.

Then find out that they're a couple hours early.

The system probably displays the flight time for the boarding crew when they scan the boarding pass, but they're trying to get everyone on and seated so they can get out on time, so they probably barely glance at the screen, making it easy to miss. Really I can think of only two solutions, one of which is more a joke...

1. Fewer flights, and give the crew more time to load people, including checking the boarding passes thouroghly...

2. Set up the scan terminal to really alert someone if anything doesn't sync up. Boarding pass has a flight time of 12:00 but it's 9:00? Flash red and beep! Wrong flight entirely? Flash red and beep!