Best Practices of managing the B2B and Drop ship POs against the uploaded open Sales Orders

Summary

Best Practices of managing the B2B and Drop ship POs against the uploaded open Sales Orders

Content

We are uploading the Open Sales Orders to the system which has both Drop ship and back to back items.So when I load ,system will create requisitions and then POs for the Back to back and Drop ship Sales orders.But in reality customer could have given POs from legacy to their suppliers ,so what is the best way to manage system generated POs vs their Legacy POs? Ovbiously we needs our cloud generated POs for downstream applications ,so in practical world do they ask their suppliers to cancel the legacy POs and refer to our cloud generated POs? and Customer