While I do require a postcode for such shipments, it's not used for shipments that would be tracked via postnl.post. It's either like this or making two PostNL courier entries and requiring the user to decide which is the right one.
If you have a non-working tracking ID with the current system, please supply all relevant information (including postcode and target country) to deliveries@orrs.de so I can figure out what needs to be changed.