Prospector. You have a touching faith in the skills of the accident investigators. Believe me they are not perfect. The absence of meaningful investigation into the role played by the VASIS in the Mount Gambier fatal accident proved that.
Re PAPI limitations. Like T-VASIS and other navigation systems such as red - white VASIS. They are all likely to produce erroneous indications in fog or mist and the systems cannot necessarily be relied upon in these conditions. In the brochures for these systems you will find no mention of these limitations.
The fact that a previous crew made no comment about the Christchurch PAPI means nothing at all. When they became visual they would have been glued to the ILS glide path either on automatics or partial automatics and flight director. They would have no time to look at the PAPI and with speeds around 130 knots over the fence it is doubtful if they would have time to compare PAPI and ILS glide indications. In any case it is possible that the PAPI and ILS glide path transmitter are sited differently.
In several mysterious CFIT accidents over the years where the crew have flown into the deck at night on final approach there has been little said in the accident reports of the possibility of erroneous light signals from VASIS - if indeed the weather conditions were conducive at the time. The Mount Gambier accident revealed that local pilots operating into Mt Gambier had frequently experienced gross VASIS light signal errors in mist, but for some reason no one thought it of much consequence.