Terminology 

ATP (Available to promise):  is a critical calculation used in supply chain management, manufacturing, and fulfillment.  In a nutshell, ATP calculations is used in SAP to control the proportional distribution of your products among your customers

GI (Good Issue): Goods Issue is basically movement of material/products within the plant for consumption/manufacturing or outside the plant as delivery to Customer. Goods issue from the Warehouse Management system (WMS) is the physical issue of goods or materials from the warehouse. Goods issue posting results in a decrease in stock in the warehouse.

To be Issued Date

To be issued date is used to know when an order line will be billed. This concept is used for the Open order and the Shipped but not billed part. To be issued date can be calculated only if the sales order generates a delivery document. That means the credit/debit memo are not included in the Open order and the shipped but not billed part. The returns are not considered in the Open order and shipped but not billed part. (ask Saints)

To be issued date is calculated according to the most updated document in the document flow (shipment document, delivery document or sales order document).

1. The delivery document if the quantity is issued or not issued.
2. The shipment document*.
3. The sales order document at the schedule line level.

(*) A shipment document can be created without the shipment dates. In this case the shipment document will be ignored in the determination of the To be invoiced or the To be issued date.

Rule follows the hierarchy below: 

1)  Actual Good Issue date.

If a delivery document exist with an actual GI date. to be issued date (Ask Diago)

2) Shipment completion date (planned or actual) 

(Shipment document exists and the delivery is not issued)

3) Delivery Planned Goods Issue date 

(Delivery document exists without an actual Goods Issue date)

4) Scheduled Goods Issue date of the order line (at the schedule line level)

(Shipment & Delivery document do not exist)

First and Last Requested Goods Issues Date

With ATP

First requested Goods Issue date 

    = First requested delivery date - (First ATP - First ATP GI date)

Last requested Goods Issue date 

    = Last requested delivery date - (Last ATP - Last ATP GI date)

Without ATP

First requested Goods Issue date 

    = First requested delivery date - Transit time

Last requested Goods Issue date 

    = Last requested delivery date - Transit time

Important note: First ATP date can be updated if there are changes in the quantity of the order line or in the Requested Delivery date or in Material

To Determine The To Be Issued Quantity (The Rest To Be Delivered)

The rest to be delivered is the quantity which need to be delivered to the customer to complete the requested quantity. The rest to be delivered is defined at the schedule line level. It is used in the Open order part, to determine the to be invoiced/issued quantities and the values. The calculation is done following the rules below:

Calculated at schedule line level

Important note: If the rest to be delivered < 0, the value is forced to 0.

(Case, delivered qty > confirmed qty)