it will not separate it.
Let's say that you loaded data to Product 1 and Product 2, then they were aggregated in Planning.
If you drill from Total Products, ERPI will not find any intersection for Total Products as you were not loading data to that intersection.
You will be able to drill-through from Planning to the intersections you loaded data with ERPI (intersection for Product 1 and Product 2)
Think of drill-through as passing the intersection details from Planning back to ERPI. If ERPI does not find that intersection, it will show an error.