Gst itc claiming

You cannot claim ITC for the period July 2017 to March 2019 as last date for claiming such ITC is already went... you can claim ITC for the period April 2019 to March 2020..

Thank you sir

Can u explain how we have some purchase bill of 2019 on which input tax does not claim till now?

Can I have that official notification for that

You can claim input tax credit of purchase bill of F.Y 2019-20 in GSTR 3b return up the return of September 2020
But you can't claim ITC of purchase relating to F.Y 2018-19 as the due date for claim of ITC is already expired.
So, if your purchase bill are after 01 April 2019 than you can claim it in 3b return up to September 2020 return.

From where we can get official notification about expiry date for claiming such itc

As per the provision u/s 16(4) of CGST Act, 2017, a taxpayer can take input tax credit in respect of any invoice or debit note for supply of goods or services or both before the due date of furnishing of the return u/s 39 for the month of September following the end of financial year to which such invoice or invoice relating to such debit note pertains or up to the filing of relevant annual return, whichever is earlier. The extract of the said section is reproduced below for easy reference.