SPN is only a fictitious archive, and the document ID number is structured so that the first four digits tell whether it is a shipment for supplier return (SRT), stock transfer (STW) or a shipping advice (CSA). 

The last six digits reflect the ID number of the specific document.

If several documents are linked together in the shipment application (SPN), the document ID number the Shipment (SPN) is based on is used.

 

Example: if the first four digits are 3100 = STW (Stock transfer document), the following 6 digits will be the ID number of the specific document.