Flightaware has actual loaded flight plans. These flight plans re for instrument flight plans which all airline flights are. They tell ATC to expect them. They activate the plan once they are ready to go in the cockpit and get their actual clearance to go. Sometimes the flight can be cancelled after the flight plan is loaded. Typically a flight-lan expires two hours after scheduled departure unless the pilot/airline calls/uploads delayed departure time.

So if a plan looks 2 hours old +, it usually means they haven’t communicated the delay.