I see the Pink and White Terraces have been discovered again. In this case it would be very easy to confirm the location one way or another. All that is needed is for a helicopter to fly in a portable drilling rig and to drill the land over the alleged site. The drill cores would confirm the location one way or another.
It should possibly take less than a day at a cost of say $10,000.
Possibly a benevolent business might be prepared to put up the money or iwi may wish to fund it.
In the case of the other two locations which have been identified as being under the lake, that again is simple to confirm.
Just lower the lake to its original levels prior to the eruption. If the terraces are still there then they will be revealed in all their glory. If not, so what. The eighth wonder of the world. The returns in terms of tourism would far outweigh any costs as the cost again would be minimal. Historically that has to be the decision of iwi.