Note that this is a deadline for the gate, not check-in

DL's deadline is T-45 for international. Yes, GA's can see who is connecting and who is originating.

The only reasons gate times matter are:

1. Flights to the US where security or secondary security is at the gate. Dependong on the station, late pax may not get processed. Some places just stick to the rules because it's easier.

2. At T-45, if the flight is overbooked and at risk of an oversale, the GA may offload no shows. Whether that matters now that DL is offering larger VDB's and thus has a reason to offload no shows won't be known for a while.

3. Early departures. Clearly not 45 minutes early, but once the 45-minute mark has passed and everybody at the gate has been boarded, the flight can close and push and you are SOL.