Most of us take grit size with a grain of salt. Besides all of the permormance variable, friability, sintered, type of resin etc. Then the grit size itself is a moot point altogether depending on how the manufactures seperate the particles. i.e a 5 micron particle can pass through a sieve and be 10 mcrons long. As long as manufactures use their own methods of grading, there will never be truthful standard and realistically as long as the particles are bound in stone it would be misleading anyway.
All part the fun of trying out new hones.