Within a Sales Line, there are 2 fields which are linked to the Purchase Order. These are:

• Purchase Order No.
• Purch. Order Line No.

and

• Special Order Purchase No.
• Special Order Purch. Line No.

These fields are filled in depending on whether the line is a Drop Shipment or a Special Order.

This is legacy code from (possibly from Navision Attain v3?).

A Sales Line can only be linked to 1 purchase line (unless this BC idea is completed: (https://experience.dynamics.com/ideas/idea/?ideaid=17188a2a-de09-ee11-913a-0003ff45ce96) In addition a line can either be Drop Ship or Special Order (not both at same time) See "Purchasing Code" field, and code in Table 5721.

Therefore, it makes sense to amalgamate these fields into 1 set. This would make it simpler on user (no need for two buttons to show the Purchase Order from the Sales Order), plus makes code simpler to maintain/write. For example, if in code you want to find a Purchase Order from a Sales Order, you must check which value is filled in and use the correct field - with one field it simplifies this.