PBL
In any case, your factor wouldn't affect the *sudden* jump in apparent "saves" which occurred with the introduction of TCAS, since nav equipment precision has evolved, rather than jumping spontaneously and coincidentally with the mandate for TCAS.
I see what you are saying, however (in Europe anyway) whilst nav equipment precision has been evolutionary, adoption of it has not.
At the lower / middle of the commercial air transport sector the B-RNAV mandate caused a sudden step change improvement in accuracy. On the fleet I was flying at the time we went from blundering around on VORs 100 miles away to using GPS with observed typical ANPs of .07 miles (or better).
E.G. If memory serves that was '98? and I went straight from being on the team introducing our FMS (for B-RNAV) to being the lead guy on our TCAS implementation for the ACAS mandate, which was in and operational by the end of 2000 ish
Hence, my (admitably insular) viewpoint is that we had a radical improvement in nav accuracy almost concurrently with getting TCAS.
pb