Updated return time limit extended; filing barred after late show cause notice, except where notice is found unfit. The amendment lengthens the period to furnish an updated return under section 139(8A) from twenty-four months to forty-eight months from the end of the relevant assessment year, while adding a proviso that bars updated returns if a notice to show-cause under section 148A is issued after thirty-six months from that year-end; however, where an order under sub-section (3) of section 148A finds it not fit to issue a notice under section 148, the filer may submit an updated return up to forty-eight months.