Extension of due date for filing Form GSTR-4: statutory deadline amended and deemed to have retrospective commencement. The Government amended Notification No. 21/2019-State Tax by substituting the earlier due date for filing Form GSTR-4 for FY 2019-20 with a later date in the proviso to the third paragraph; the amendment is issued as Notification No. 64/2020-State Tax and is deemed to have come into force from the earlier deadline.