To help find possible data inconsistencies, 2 more views that will show duplicate entries were added in the same manner as the existing "Duplicate Orders" View under "Orders":
added View "Duplicate Purchase Orders" under "Orders"
added View "Duplicate Invoices" under "Invoices"
Duplicate Orders View will list all Orders where the Order Number is found more than once. The same filtering is done for Duplicate Purchase Orders, the same PO Number more than once; and Duplicate Invoices, with the same Invoice Number more than once.
This filtering happens regardless of the Date for each of those items, so the same Order Number that occurs twice on different days would be shown... In some (perhaps odd) cases this might be normal and can be ignored. In some cases, that might be exactly what you were looking for. This is the purpose of Views, to help the User find entries which may otherwise be difficult to locate.