Are you sure they haven't moved the dividing line? They do change territories to balance work loads, etc.

In my experience, the radio frequencies change at the dividing line so the dispatchers don't interfere with each other. It's unlikley that a dispatcher would have a frequency for a territory he is not working. There are signs on the right of way to remind crews to change frequencies.

It's also possible that the territories change on weekends, at night, etc. when work loads would be lighter.