Why are some POS transactions in my store classified as N/A?

Hi,

We use shopify as the POS for card transactions in our store - some customers seem to get classified as first time or returning cusomers (and given the customer name Valued Customer Valued Customer) but the majority go through as type N/A and name N/A.

Can anyone explain what is the difference between these transactions and whether I can change anything to get a better steer on repeat purchase (i assume via the credit/debit card)?

Thanks!