Last Date of Filling GSTR-1

last date for filing GSTR-1 31/10/2018 for Sept month return.
2.Also as per section -16(4) of CGST act last date for availing credit or amending invoices would be earlier of following :
Due date for filing September month return following end of the FY. or
Due date for filing annual return.
so last date was 31-10-18...

Hope same will clarify ur doubt.

Thank You So Much Sir 🙏