The words "previous year" under Income Tax Act means the financial year in respect of which the income is to be assessed. The Income Tax return for the financial year 2014-15 has to be filed within the due dates, as applicable to the classes of assessees, during the financial year 2015-16, which is called " assessment year" relevant to the previous (financial) year 2014-15.
If the return is not filed within the due date, then it can still be filed as "belated return" on or before the 31st March succeeding two years from the end of the previous year. Thus the return for the previous year 2014-15 can be filed as a belated return on or before 31st March 2017.
As a corollary, the return for the financial (previous) year 2013-14, can be filed as a belated return on or before 31st March 2016. The return for the financial (previous) year 2012-13 and earlier cannot be filed now.
Normally the need for filing returns voluntarily for the previous years beyond the time allowed even for belated return arises when there is a claim for refund, which could not be claimed for some genuine reasons. In such case, the refunds can be claimed u/s 119(2)(b) of the Income Tax Act, subject to fulfillment of conditions specified there under.
There is tax liability but return is not filed for some reason or other. As the time limit is over even for filing of belated returns, there cannot be voluntary filing of returns. The Income Tax Department has powers to issue notices u/s 147/148 requiring the assessee to file returns, if in its opinion, income has escaped assessment, even if a return is filed and assessment is completed. There are time limits for issue of notices u/s 147/148, depending upon the quantum of the tax liability and the maximum time limit is 6 years from the end of the relevant assessment year. If the assessee genuinely wants to disclose his income for the past years whether he filed return or not, he can request his assessing officer to issue notice u/s 147/148 to enable him to file his return. By doing so, he can get sympathetic consideration in levy of penalty and prosecution.
Generally the need for filing returns for 3 years arises, when a person wants to take loans (mainly housing loans). Returns can be filed for the last two years by efiling. The return for 1st year cannot be filed voluntarily because it is time barred. The practical solution in such a case is to e-file the return, indicating that the return is filed in response to notice issued by the Income Tax Department. The return gets uploaded and acknowledgment gets generated. This should be sufficient evidence for the filing of return for the first year also. As the tax is also paid, if applicable, the return may get processed by referring to the jurisdictional ITO, in which case, the assessment proceedings may be taken up u/s 143(3), depending upon the facts of the case.