You can watch this video, I was trying to explain the qualification rules for cross server GNW

https://streamable.com/te9y4

Basically, the rule says top 16 from each server are eligible to be selected in cross server gnw; after that according to the rules as well all eligible groups from all servers in the same cluster will be sorted into categories according to the winning situations so its (winners -> runner ups -> third place -> etc) then each category is sorted by power.

You can check what i just explained and see the advancement ranking from the normal gnw npc (you should fine it under tournament).