PL (CTCSS) output with defect detectors

I had a post awhile ago, maybe there are some new members who might have an answer.

Is/was there an industry standard, or specific railroad standard for outputting a PL tone with defect detectors on a no-defect or defect detected? On the ex-CR Southern Tier near me, a PL of 100.0 is transmitted and correctly programmed railroad spectra's are capable of displaying "NO DEFECTS" on the display. The railroad spectra is able to decode up to two PL tones for this feature. I have not figured out the "defect" PL is for these detectors.

So in short, does anyone know what PL's for what message are used by who/where?

Conrail used to use 100.0 for "no defects" and 150.0 for a defect alert. The 150.0 was eliminated several years ago by
CSX in former Conrail territory and now the 100.0 is also gone from most detectors in my area as they have been upgraded.

The 150.0 is not a standard PL and it and the 100.0 used to be generated by the detector. I believe they began to eliminate the use of special transmitters in the detectors to use regular mobile radio transmitters instead which could only encode a standard 100.0 PL tone and then it was later decided to just eliminate the tone.

The detector PL feature in the clean cab radios was to prevent transmissions while the detector was "talking". The 100.0 was also originally used to trigger a recorder at the dispatch center and the 150.0 to alert the dispatcher. All of these features
seem to be obsolete, at least on CSX, so there is no tone on most detectors now.