Order Forecast and MRP

We are having trouble understanding forecasting sales. We can create
the forecast fine. The problem comes when we forecast sales for
multiple customers for the same manufactured part. If one Customer
buys more than the original forecast it will begin consuming the other
customers forecast.

This would be fine from the perspective that forecasting is really
there to drive MRP. But we also want to understand what our customers
are doing. If a customer is not buying to the forecast they provided
we may not know if another customer is buying more than theirs and
consuming it.