¹[15.  Return after due date and amendment of return.— If any person has not furnished a return within the time allowed under sub- section (1) of section 14 or under a notice issued under clause (i) of sub-section (4) of section 16, or having furnished a return discovers any omission or wrong statement therein, he may furnish a return or a revised return, as the case may be, at any time before the expiry of one year from the end of the relevant assessment year or before the completion of the assessment, whichever is earlier:

    Provided that—

   (a)  where such return or revised return relates to the assessment year commencing on the 1st day of April, 1987, or any earlier assessment year, it may be furnished at any time up to and inclusive of the 31st day of March, 1990 or before the completion of the assessment, whichever is earlier;

   (b)  where such return or revised return relates to the assessment year commencing on the 1st day of April, 1988, it may be furnished at any time up to and inclusive of the 31st day of March, 1991 or before the completion of the assessment, whichever is earlier.]