I just wondered when you get Concoction Ranks 4, 5, 6, 7 and 8. Some of the alchemists have almost reached 1000 (saying no names) but still are stuck on Concoction Rank, as the #2 has 450-something but still not Concoction Rank 4.
Is it because of the potions from 5 and further are too OP so that they can not be used on this server? I'm just curious since I was excited of the Potions of Decay and Resistance.
Please respond!

A Skill in Alchemy that lets you use more brewing ingredients depending no what Concoction Rank you are currently having.