Unsure about lapping

[Dramadon3151]

So I recently got a 120 micron diamond plate, as I broke my lapping plate. I used this once in my stones, and they all got nice and flat, but my higher stones, seemed to be a lower grit quality after....is that possible with shaptons? I mean it's a synthetic stone with pre decided grit particles. Or am I destroying my finishing stones? One thing is that, after lapping it was a bit rough, but pretty quick they smoothed out, also is it ok to use an 8k stone, as a slurry stone? Meaning, I have an extra 8k shapton, and was considering cutting a portion off to use as a slurry stone.