If you saw NX4, that suggests you are using a Uniden 436/536. NX4 = NEXEDGE48 and NX9 = NEXEDGE96. From a programming standpoint it doesn't make a difference whether it is one or the other. If you only see NX4 or NX9 and do not see any reference to a RAN, then it's likely a conventional frequency. If you see NX4 or NX9 and a RAN, that would be an indicator that the frequency is part of a trunked system somewhere.
This may or may not be of use or help to you & for you but worth a try or at least a look at. This was found on another Radio Reference Forum Thread regarding NXDN.