Debit note credit note qurey

We have received a Credit Note from our Supplier for rate difference (We have issued Debit Note for the same in our records/books).

We have also issued a counter Credit Note to our Customer fir rate difference (They have issued a Debit Note to us)

1) Do we have to show both the Credit Note & Debit Note issued by us in the GSTR1 or only the Credit Note issued by us to my customer? (as we are the seller)

2) I have forgotten to show the above Credit Note in the GSTR of May 2019. Can I show it in the next month GSTR1? i.e will the GST portal accept my Credit Note dated May 2019 in June 2019 or should I change the date of my CN to June & file it in June GSTR1?

Thanks in advance.