Even as the income tax return filing last date is first approaching, many taxpayers are not very sure about many facts. 
 
If a person after furnishing the return finds any mistake, omission or any wrong statement, then return should be revised within the prescribed time limit.
 
A return can be revised before the end of the Assessment Year or before the completion of the assessment; whichever is earlier (say assessment year 2018-19).
 
However, for the earlier Assessment Years preceding to the Assessment Year 2018-19 , a return can be revised before the expiry of one year from the end of the Assessment Year or before the completion of the assessment by the department; whichever is earlier (till A Y 2017-18).
 
If original return has been filed in paper format or manually, then technically it can't be revised by online mode or electronically.
Revised return can be filed online under Section 139(5).  
 
Since legal proceedings under the Income-tax Act can be initiated up to four or six years (as the case may be) prior to the current financial year, one must maintain copy of the return  at least for this period.
 
However, in certain cases the proceedings can be initiated even after 6 years, hence, it is advised to preserve the copy of return as long as possible.
 
Further, after introduction of the e-filing facility, it is very easy and simple to maintain the copy of return of income.
 
Amounts paid as advance tax and withheld in the form of TDS or collected in the form of TCS will take the character of your tax due only on completion of self-assessment of your income.
 
This self-assessment is intimated to the department by way of filing of the return of income. 
 
Only then the government assumes rights over the taxes paid by you. Filing of return is critical for this process and, hence, has been made mandatory and a failure to do so will attract levy of penalty.