Using Lookup but eliminating entries from new list

Using Lookup but eliminating entries from new list

I have an app which my sales team logs their sales into.  Their is a field named "Order #" on this form which is a unique number.  I have a follow up group of employees who follows up on sales from the previous week.  I have created a second app for this group and am using the lookup field to import the "Order #" from app 1.  I am able to use deluge to filter out all sales older than a week old, and to select based on the country.  But once the customer is contacted and the form is filled out (by the second agent in the second app) I want that "Order #" to no longer be available for selection in the future.  basically, the only selectable entries should be "Order #"s which have yet to be recontacted.  How can I accomplish this?