In the backorder processing function, you are given a list of receipts and issues for a particular material that are relevant for the availability check. Missing parts occur if a requirement (sales order, reservation, and so on) could not be confirmed or could only be partially confirmed in the availability check according to ATP logic; the confirmed quantity is less than the requirements quantity.

Material shortages may occur for one of the following reasons:

• The quantity of a sales order cannot or can only partially be delivered on the required date. Therefore, the sales order has not been confirmed.
• The desired delivery date of a sales order lies outside the replenishment lead time. Therefore it is confirmed, but the quantities have not yet been procured.
• A dependent reservation has not yet been confirmed.

You are recommended to set a missing-parts checking rule in Customizing for MRP in Maintain all plant parameters ® Checking rule backorder updating.

• Open requirements can be reconfirmed, for example, if stock has increased since the last availability check, if a new receipt has been made, and so on.
• Quantities that have already been confirmed can be redistributed whereby the quantities of confirmed requirements may be either partially or completely reduced and then allocated to an alternative more urgent requirement.