Deduction denial for late return filing limits unit tax benefit where export proceeds are not repatriated timely. Provision added to section 10AA denies the unit deduction if the return of income is not furnished by the due date; applicability is further conditioned on receipt in India of export proceeds in convertible foreign exchange within six months of the previous year's end or within an extended period allowed by the competent authority, with export turnover defined to exclude certain charges and deemed received where credited to a separate RBI-approved foreign bank account.