"that assist in classifying pots"这一部分是定语从句部分,用来修饰Long descriptions .
that assist in classifying pots的中文解释是：有助於分别 / 区别不同的瓷器类型.
这个从句部分放在exist的後面是为了避免这个整句的头重脚轻：
Long descriptions of the different types of ware that assist in classifying pots exist,although- - --.(exist在後面,句子显得不平衡,头重脚轻.)
你的句子也可以,并且最好这样rewrie :
There exist long descriptions of the different types of ware that assist in classifying pots,although -- - -.