Credit and debit notes govern post invoice tax adjustments and reporting, with supplier liability adjustments subject to prescribed conditions. Section 34 allows suppliers to issue credit notes when an invoice overstates taxable value or tax, on return of goods, or when supplies are deficient, and requires declaration of such credit notes in the monthly return or by the specified annual deadline, with tax liability adjusted as prescribed but not reduced where tax incidence was passed on; it also requires issuance and monthly declaration of debit notes (including supplementary invoices) when an invoice understates taxable value or tax, with prescribed particulars and prescribed adjustment of tax liability.