As a GM I do not need to know the special abilities of PCs. The player will probably tell me, when it becomes relevant. That's a great advantage of a class based system, assuming it works: Make an adventure for third level characters and you do not have to worry what characters will appear. That's the theory at least.
Still, a game needs consistend rules / guidelines for GMs, as you say.
Still, a game needs consistend rules / guidelines for GMs, as you say.