For Q1: It sounds like you might not be the reseller of record for all of their systems. If you put in the serial number of one that doesn't show up and can't see it, that would be the most likely case.
You can request that is changed by opening a ticket via https://mysupport.netapp.com/eservice/assistant for category 1 = AutoSupport, category 2 = Active IQ, and provide a list of all systems you know about from the customer, and all you can see, and ask to be made the reseller for each of them. Please provide a customer contact in the request and they will sort it out.
For Q2: I'm afraid I don't actually know the interface you're referring to here. I would suggest you refer to your partner TPM or solutions center to see if there is an easier option. Please feel free to message me with your corporate contact details if you'd like me to put you in touch with them.
Hope this helps!