Can you remove the radio from the aircraft and connect it directly to a computer to determine and set the NetID? Apart from guessing that’s the only way you will find the NetID
Or I guess you are still trying to the one to many thing…
If you know the NetIDs of all the airborne radios, then you could keep changing the NetID of the ground radio to communicate with the different aircraft - but that gives you a substantial black-out period for each aircraft.