That's what I meant; I probably didn't type it right.
In the Old Timeline:
Janus-1 enters gate.
Janus-1 travels through gate.
Janus-1 exits gate.
In the New Timeline:
Janus-2 enters gate.
Janus-2 travels through gate.
At threshold of exiting gate, Janus-2 is TB'd and Janus-1 exist gate.
If TTI states the last exit from a gate is what is preserved, then Janus-1 would only appear at the exit of the gate, meaning that Janus-2 would be experiencing entering and traveling through the gate. Janus-2 would also see the exit, and reach it...but never exit. Janus-1 takes over that part of the job.
Bad graphical example:
ENTRANCE TO GATE MID-GATE EXIT--|
22222222222222222222222222222222222222222222222222222222111111111111111
I knew Janus-1 would exit, but it just doesn't make sense for Janus-2 to enter the gate, and then be TB'd at that moment, with Janus-1 traveling. Janus-1 shouldn't appear until the actual exit from the gate. Which is why I questioned how the statement arose that the gate was sending them to the DBT. I took it to be the gate was activated to preserve TB, and therefore was to serve the same purpose. The actual "exit" from the gate is what TB's them, not the gate itself.
The only way I can explain this decently is imagine one of those oval shaped mirrors on a frame off the ground; those ones that aren't on a wall, kinda in the open. Imagine that only the frame is there, no glass, and it's straight up and down. Janus-2 walks up to it, and goes to step through. As he passes through the frame which would hold the glass for the mirror, he is replaced with Janus-1. He does not get replaced as he is walking to the mirror, only when he goes "through" the frame.