GST registration

where it is written ? 

I have a doubt can anybody clear? One of my client is a wholesale distributor, and in his return its showing only GSTR6. Should he ask for and amendment for GSTR1 and GSTR3?
2) The manufacturer or the seller of my client has filed and the credit amount and invoice is auto populated in GSTR6A, if we file GSTR6 can the retailers take credit?

Distinct Person means who has more than 1 businesses... every business is treated as distinct person..