Loss return validity: late-filed loss returns within permitted extension must be processed and assessed, with carry forward status recorded. Where a loss return under business or capital gains is filed after the period specified in section 139(3) but within the extended time under section 139(4), the return is valid; the ITO must take cognizance, complete assessment within the prescribed time limits and state in the order whether the loss will be disallowed for carry forward. Prior Board instruction held that unabsorbed depreciation and development rebate can still be carried forward despite late filing.