PO Number, PO Date, Terms and Order Instructions have been added to all of the Sales listings -- Orders, Order Line Items, Invoice, Invoice Line Items, and Payment Line Items -- so that the PO and any notes can be followed all the way through from Order to Commission paid
If your Agency's primary key for tracking Customer engagement is the PO, Users can access that field in all of the Sales listings. This makes it very easy to filter and sort by PO Numbers and Dates in all of the screens, to find what you are looking for.
Order Terms and Order Instructions are more free-form fields that are used in various ways by different Agencies. The "Terms" can be the delivery and payment terms as captured from the manufacturers' reports, or can be more generic notes as added by the User. The same applies to the Order Instructions as either a miscellaneous field captured from a report -- and can certainly be different fields from each of the Manufacturers -- or simply notes about the disposition of this particular Order.
The key is these entries will follow the Order through its lifetime in the system.