26 October 2017
without any doubt you can claim ITC on Unclaimed purchases in GSTR 3B.
see GSTR 3B is a Provisional return showing Total of Sales & Purchases & no invoice number of proof required for filing GSTR 3B.
and whatever the sales figure mentioned in GSTR 3B for that we are filing GSTR 1 details of Sales invoice wise.
and for these purchases in GSTR 3B we are filing GSTR 2 .
So you can accept purchases reflecting i. GSTR 2 which you forgot to enter in GSTR 3B.
The same input will be available once GSTR 3 is filed & input will be showed in Electronic Credit Ledger.
Pls let me know if you have any further questions