Hello. Thanks for your hard work and I pray that you and your country will continue to recover rapidly.
Can you tell me if it could be useful to do the procedures described above or do you know any other and more accurate “clinic-made” tests?

I am not aware of any “clinic-made” test in terms of the ways you described. However, if the respirator passes the fit testing then one can reasonably assume that it blocks 95 percent of particles that are 0.3 microns in size or larger. Here are some studies on this: A & B.

Can you explain to me a better and accurate difference between the two codes?

Yes. I also had to look this up when I was going over the numerous KN95 certificates. I think that these two links answer most of your questions: A & B. In the USA, 3M masks are certified by two organizations: NIOSH and FDA.

I hope this helps. Thank you.

P.S. We are working on a N95/PPE marketplace website that can help clear up some of these issues. I Will let you know when it launches.