2.
Sub-section (2) of Section 34 prescribes a time limit for issuance of credit note. It is reproduced as under:
(2) Any registered person who issues a credit note in relation to a supply of goods or services or both shall declare the details of such credit note in the return for the month during which such credit note has been issued but not later than the thirtieth day of November following the end of the financial year in which such supply was made, or the date of furnishing of the relevant annual return, whichever is earlier, and the tax liability shall be adjusted in such manner as may be prescribed:
Further, the proviso to Sub-section (2) provides that no reduction in output tax liability of the supplier shall be permitted, if the incidence of tax and interest on such supply has been passed on to any other person.
In your case, since the time limit is also exceeded, credit note declared in returns and tax cannot be adjusted.