Apologies for long delay, could you please post your question on this ? or please forward it to email@example.com. I would have it forwarded to concern team and have your question answered.
Sander, I find s/n 231508000476 is registered to a Hotel (I can't say which one here), and the other s/n is not registered.
If you are not working with a Hotel, I would contact the folks you bought the ZDs from and get proper documentation of their original POs. You would need this to register the ZDs to get support for firmware upgrades, knowledge base articles, etc.