Default assessment power: Commissioner may assess unpaid or noncompliant tax and issue notice, with objection rights preserved. The Commissioner may, for reasons recorded in writing, assess or reassess to the best of his judgment the net tax due where returns are missing, incomplete, incorrect or non compliant, and may assess unregistered persons for liable periods and subsequent periods; a notice of assessment must be served and further tax assessed is due on the date the net tax was originally due, with a right to object under the Act.