Attrition casualties in your own country are not counted in the casualties overview. Only attrition casualties that occured during sieges of enemy forts are counted.

I believe it is because for the AI attrition is calculated per stack, and there are at least 5 stacks there, none of them being large enough to suffer attrition individually.

A player cannot cheat attrition in the same way.

R5: Mamluks are resieging a fort (and have been for 3 months) with a death stack of 64k men. Yet they have not suffered any attrition in this war yet. Can somebody explain to me why?

Bug with attrition?