Class and certificate explanation:
I see many players who seem confused about the class and certification system and was asked about it:
Let me explain it this way.
Lets say in the beginner classes there is Fooj, Fuji, Fooji and Fushi. Those are classes. Some of them meet the same requirements.
Certificates are the max amount of a certain class that can exist at any given time in the game.
For example in this Fooj would have 3 certificates aka the max of it, Fuji 4, Fooji 2, Fushi 5.
As you rank up your stats and unlock more advanced classes in the other tiers the certificate requirement (Aka class limit) gets more narrow.