Only if they use the same port (20595)
Stun works a certain amount of people. Problem is restricted networks such as schools, shared ip adress for instance my ISP only gives me access to 1/4 of all ports out of 65536
For new games ipv6 helps as well as having the money to host games on dedicated servers. There was some attempt at dedicated servers by elexis then by wraitii but both ran out of time / motivation