Maybe with the data we can figure out what portion of military flights are included?
For the helicopter training flights that I notice most often, it's still rare to see one that broadcasts ADSB, probably <10%. C-130s usually don't either here but it's more often, maybe more like 25%. Perhaps for other categories of aircraft they've installed more transponders. But in the city where I live, even passive mode-C MLAT is probably around 50% success on tracking military flights for ADSB Exchange. FlightAware might have better coverage for mode-C. mode-C can't contribute to this GPS reliability data anyway but it illustrates that even C-130 pattern practice is sometimes "stealth" from a radio perspective due to the low installation rates for ADSB and difficulty of good mode-C coverage.
The paper linked elsewhere (https://web.stanford.edu/group/scpnt/gpslab/pubs/papers/Liu_...) mentioned issues with military training flights resulting in spurious low-NIC cases but unfortunately doesn't quantify it. With the way the AF rollout has gone it probably depends on the specific installation, command, and aircraft type.
In the border region specifically we would tend to expect the majority of non-military flights to be civilian CBP aircraft that aren't performing unusual maneuvers. CBP has a somewhat complicated and limited authority to disable ADS-B that I don't know the contours of, I'm not sure how often they do so on their larger (non-sUAS) aircraft. Involvement of the Air National Guard in the Texas area might complicate the analysis though.
I can actually receive high flighting planes over Del Rio so it would be interesting to see if they are reporting bad NIC values.
Military aircraft on military maneuvers don't deal with FAA ATC, the military has its own controllers. It's mostly an issue when they're operating near civilian airports (or the many, many military facilities that share an airfield with an airport). There are still adverse safety impacts to the lack of ADSB on many military aircraft, in that it defeats things like TCAS.
Actually this topic is slightly complex and I think a lot of people have misconceptions, so let's lay it out. These rules have gotten stricter and stricter in recent years.
1. ADSB is not required. Meaning, there is no universal requirement that aircraft be equipped with ADSB, and plenty of aircraft still legally operate without.
2. ADSB is required in class A, B, C, in many cases in class E, and within the "Mode-C veil" surrounding major airports.
3. ADSB is required in any case where a transponder is required, for those edge cases that are not included in the above.
4. The result is that the areas in which you can legally operate without ADS-B are mostly limited to low altitudes in rural areas. Of course, this encompasses a large portion of hobby aviation especially, but not very much commercial flight.
e; oh wait you said passive MLAT off Mode C, that makes more sense then
