If a vendor files their GSTR1 or IFF after the due date, the transactions will appear in the following month's GSTR 2B, not the original month's. This is because the GSTR 2B for the original month is typically frozen shortly after the due date. Suppliers can still claim ITC on a self-assessment basis.
If any vendor has filed GSTR1/IFF after due date , For Eg : June month GSTR1 due date was 11th July and vendor has filed it on 17th July , then in this case june transactions will be reflected in July GSTR 2B or June GSTR 2B? since June 2B is already created.