If my memeory serves me correctly (and correct me if I am wrong) I think the BK117 incident wasn't really an inadvertant IMC per se. Returning to the sunshine coat, NVFR and weather deteriorated with little warning at the destination with insufficient fuel to go anywhere else.
Crew made a descision to conduct an instrument approach into the destination...the pilot had a military instrument rating previously so at least had the skill sets to safely handle the situation in a controlled fashion......maybe it was advertent IMC
Is that in the ballpark?
Cheers
PS....Can you still operate NVG below the LSALT when considered operationally required?