The system can alert users when creating or updating an order with a Media number that is already in use in a different order.
Configure from: Administrator > Web Administrator > Configuration > Defaults > Alert duplicate Media numbers switch (fig 5):
When on, the system will alert the user when creating, importing, or updating an order with a Media number that is already in use in a different order:
The system will not prevent entering the same Media number. The user will only be alerted.