Dear Aey,
As I checked in SAP Production historical data, I saw BTH created few export sales orders with reference to BSA PO that sell back some products to BSA.
I believe previously CJ thought to use Sales Order for return process due to the performa invoice required for export process.
Could you recheck with Logistics and Purchasing Team again if they are using the right transactions for purchase return?
Let us know if you required further clarification.