Return Quantity Vs Returnable Quantity
The SAP S/4HANA Fiori app Manage Customer Returns is the central application to process customer returns. As a returns and refund clerk, you can create accelerated customer returns with reference to a preceding document, such as a sales order or an invoice.
When creating a customer return with reference, you need to select a reference document first. For each customer return item, you must enter a quantity that needs to be returned. The returnable quantity of each item is calculated by subtracting the already-returned quantity from the original quantity of the reference item.
However, with the current design, the system will not stop you from entering a quantity larger than the returnable quantity. When you do, you can complete your creation successfully without being alerted by any information message.
This is a by-design logic not a defect.
The reason behind is that there are cases where multiple customer returns can refer to the same reference document. Here, the reference document only serves to create a customer return (not really as a reference). In such cases, the return quantity doesn't have to be relevant for the reference document, and therefore you can enter any quantity according to your actual needs.
With CE2002 release, an information message notification is available to catch your attention when you enter a quantity larger than returnable quantity.