Limitations on Assessment and Collection

(a) The amount of any tax imposed by this article shall be assessed within three years after the return is filed. For the purposes of this subsection and subsection (b), a return filed before the last day prescribed for the filing thereof, or before the last day of any extension of time for the filing thereof, shall be considered as filed on such last day.

(b) If the taxpayer omits from income an amount properly includable therein which is in excess of twenty-five per cent of the amount of income stated in the return, the tax may be assessed at any time within six years after the return was filed.

(c) Where no return is filed, or if a taxpayer shall fail, when required, to file an amended return, the amount of the tax due may be assessed at any time.