Courtney, I was thinking, as I posted that, of the matter of system integration. The comments preceding it indicate certain RF spectra and aspect where the F-35 appears to be more difficult to detect, and others where it isn't as difficult. Most IAD systems have more than one sensor.
Sensor fusion, such as the CORT refit for the USN's FFG-7 class frigates (IIRC, Ingraham was the lead ship to get that refit) took the same basic sensors that got the frigates dubbed "Helen Keller" (deaf and blind) and by fusing the sensor suites (and using better computing equipment) made it a viable player in the NTDS link, in terms of track quality and confidence in tracking, particularly in the AAW/Air Defense role. That was going on 20 years ago.
It's not much of a leap to believe that other services in other nations try their hands at sensorand network data fusion to get rid of potential blind spots created by RF spectrum issues, lobes, scatter, and a dozen other detractors to RF signals getting the gain needed to separate valid from invalid returns.