Well you must be much cleverer than me Manchester because I can find no mention of the contract regarding aircraft spec and night capability - the only mention I can find of NVG is here
Between June and August 2015 work was carried out on EI-ICR to incorporate Night Vision Imaging System (NVIS)-compatible components into the aircraft. This work was carried out under an amendment (No. 13) to the contract between DTTAS and the Operator. Components were installed as part of a planned adoption of NVGs (Night Vision Goggles) by air crew. The work had the effect of changing the lighting environment within the cockpit to optimise it for use with NVGs, in particular by altering the intensity and tone of cockpit lighting and its colour spectrum. At the time of the accident the use of NVGs by crews had not commenced.
Indicating that a contract amendment was made (so not stipulated in the original) and enough money was found by DTTAS (Dept of Transport) yet it never went operational and it seems therefore that the crews were never trained.
Now there may be many reasons for that (not contained in the report) but the UKSAR S-92s were procured and utilised with NVIS so that rules out a technical issue. Possibilities are reluctance among crews to use NVG (most not ex-mil with any experience of them) or possibly DTTAS balking at the costs of modifying the aircraft, procuring NVG and then the large training bill associated with doing night SAR properly.
An interesting line earlier in the report refers to commercial pressure to get the transition from S61 to S92 completed and the loss of 2 weeks (it calls it ITAR) training. NVG/NVIS come firmly under the ITAR banner so should the service on S-92 actually have started with NVG embodied and crews trained?