Gst file return by the customer

As a supplier you are sending Invoices to your Customer same will be purchase Invoice either to registered Customer in GST or unregistered Customer, so those who are unregistered they will not file any GST return, however those who are registered will file GSTR3B, for Input tax credit of purchase made from you, and while filling purchase invoice and obtaining input tax credit they will show consolidated purchase figures in Table 4 of GSTR3B .so it's very difficult to find out bill wise details filed by your Customer in GSTR3B.  (Bill wise details will be available to your customer only in GSTR2B / 2A   }