different concrete classes

Not sure how it looks in the US, but in Europe we have different concrete classes depending on its strength and - what goes along with that - different material ratio. Therefore, concrete class C20/25 can have different recycled content than concrete class C30/37. If we used many different concrete classes on our project (as probably every project does), shall we ask our supplier to specify recycled content for every single class, or he can just give us the average percent for a typical concrete mix?