I have three nakago with 3,3 and 4 distinct notch cuts on their edges, often wondered what they were for. These notches are all on the upper right hand side only a bit higher than the mekugi-ana but well below the habaki area.
Have one tanto with three very distinct circle chisel punches high up on the nakago which I assume is telling the generation of that smith.
There is an awful lot to learn and I feel like a tadpole in a vast Nihonto pond.