ITC Availment

For claiming ITC, One need to satisfy the following FOUR CONDITIONS as laid down under Section 16(2) of the CGST Act 2017 :

(a). Possession of a Tax Invoice.
(b). Received the Goods or Services or both.
(c). The Supplier must have paid the taxes to the Government Exchequer, and
(d). The Recipient must have filed the Return.

So filing of FORM GSTR-1 within the due date or after the due date is not the determining factor for claiming ITC. When your Supplier files his GSTR-1 (Statement of Outward Supplies), it gets auto populated in your GSTR-2A. One cannot avail ITC only on the basis that the Invoice is being reflected in his GSTR-2A. The taxpayer needs to check all the four conditions as laid down u/s 16(2) for claiming ITC.

Yes he can. Suppose there is an invoice which belong to July 2020. Supplier filed is July 2020 return on say 15 October, 2020. In this case you can take the ITC in October 2020