For the most part, these systems use the ADSB to track the ac
That doesn't make sense - it would imply that aircraft not fitted with ADS-B aren't going to be detected when they go off-track, which is clearly not the case. Ditto aircraft which send ADS-B with a low NUC_P.
The airport NTK systems that I've encountered use processed radar recordings to monitor track-keeping. That way, they capture 100% of flights.