An additional assessment or estimated assessment as heretofore provided shall be made by the department at any time within five (5) years after any net income of any taxpayer should have been returned by him for taxation, any such additional assessment or estimated assessment may be made at any time during said period, notwithstanding he shall have paid a tax assessed on the basis of returns previously made or filed, and notwithstanding the department shall have made previous additional or estimated assessments against such taxpayer. In any such case no credit shall be given for any penalty formerly assessed and paid.
72 P.S. § 3402-504