[Question]Mob drops

I know how I need to make the items have a grade, and how to find and change what different mob drops. But there is one thing I just don't understand. There are 9 different records for each mob. How does it work?

Is it something like this:
1) All the diffrent ItemOrders drops (ofc only if it adds up with the droprate)
or
2) One of the 9 different ItemOrders drops what it should (again, ofc only if it adds up with the droprate)

Thanks in advance:)

A grade is ehm an art of a dropp container, one grade dropps only that what in the grade is...

so u can put 9 grades on a mob^^

Kind of what I did mean with number 1. Thanks:)