I'll try to help out, but take this with a grain of salt.
In my opinion, they are not NILL.
They are unusual. I don't recall seeing a set like that before with the front strap covered and the flare at the upper right, lower left, and significant contouring.
Have you tried to remove them, take a photo, and do a reverse image search? This may provide answers.
Nill opened shop in 1969 and I have seen a lot of their grips and know where they had bought their wooden blanks until the wood dealer went bankrupt about ten years ago.