You are correct. There is no hard limit on lic. It’s designed for bursts of those times where you may have a influx of devices. If it happens multiple times then you can work with TAC or you local sales team to true up your lic. Just like any other software out there you do not want to violate the terms of the lic and run out of compliance.
As for subscription lic when they expire then CPPM will stop processing radius request. A perpetual lic will never stop processing requests.