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.