a. Whenever the commissioner shall determine that any tax or taxes assessed pursuant to this act were less than or in excess of the amount thereof lawfully assessable, he may correct such deficiency or error by reassessing such tax, or any part thereof.
b. Whenever property subject to taxation under this act has or shall have been omitted from assessment by failure of the taxpayer to include it in a return of information, or otherwise, the commissioner may, if he finds that such property has been omitted from his assessment, cause such property to be assessed for any omitted years in accordance with the provisions of this act.