There are many reasons a new congregation is set up.
1) They really only take jws in other congregations and make a new one. Rob Peter to pay Paul.
2) jws move in from other circuits (or have been over time) not an increase, just already jws moving in, not new jws to the organization.
3) The WTS wants to mixup a couple of congregations with problem elder bodies or families.
4) The WTS wants to open up an area with no jws and has jws from other areas move in (usually small).
A really new congregation would have to be mostly newly baptized jws...........
In my urban area there has not been a new congregation for 20 years. The deaf group and spanish have never really gotten off the ground and the deaf group no longer exists.
The only people baptized have been children of jws. If you still go to your congregation, how many have been baptized that are not children of jws? In the last 5 years?