Would it be possible for you to add a feature where you could mark a contact within a customer's profile as no longer active, but still have it connected to the past orders they were involved with?
It would be helpful for clarity of who ordered it in the past, while also making it clear that they are no longer a valid contact for future orders.
Right now, I just add that info in the "Fax" line as well with a date to try to help.