After flattening a stone with a DMT Course or sandpaper, What is the highest grit you have gone up to after that?

The reason I am asking this question is my cousin was looking at my new coticule and said they have a lapper at work that would lap it and he stated it was 16,000 grit.

I am thinking about taking him up on his offer. Do you think a stone would benefit from this?

I have already used the DMT 325, DMT 1200, and then rubbed it well with slurry stone.