(a) The amount of tax which is shown to be due on any return (including any additional amount subject to notice under § 528(a) of this title as a result of a mathematical or clerical error) shall be deemed to be assessed on the date of filing such return, and an increase in such tax which is shown on an amended return shall be deemed to be assessed on the date of filing such amended return. In the case of a return filed without the computation of the tax, the tax computed by the Director shall be deemed to be assessed on the date when payment of such tax is due. If a notice of proposed assessment has been mailed pursuant to § 521(c) of this title, the amount of the proposed assessment shall be deemed to be assessed, if no protest under § 523 of this title is timely filed, on the date provided in § 522 of this title, or, if such a protest is timely filed, on the date when the determination of the Director becomes final pursuant to § 525 of this title; provided, however, that, if the taxpayer seeks review of the Director’s determination pursuant to § 544 of this title, the amount of the proposed assessment shall not be deemed to be assessed until the expiration of 60 days (30 days in the case of withholding taxes, or, in the case of other taxes imposed by Chapter 11 of this title, 120 days if the taxpayer is outside the United States) from the first date when (i) the determination of the Tax Appeal Board under § 544 of this title becomes final and not subject to judicial review under § 331 of this title, or (ii) if the taxpayer appeals from the Tax Appeal Board determination pursuant to § 331 of this title, an order of the Superior Court of the State or the Supreme Court of the State entered upon the decision on such appeal becomes final and not subject to appeal. If an amended return or report filed pursuant to § 514 of this title concedes the accuracy of a federal change or correction, any deficiency in tax under this title resulting therefrom shall be deemed to be assessed on the date of filing such amended return or report, and such assessment shall be deemed timely notwithstanding any other provisions of this chapter. Any amount paid as a tax, or in respect of a tax, other than amounts withheld at the source or paid as estimated income tax, shall be deemed to be assessed upon the date of the Director’s receipt of payment, notwithstanding any other provision of this title.

(b) If the mode or time for the assessment of any tax under this title or Title 4, including interest, penalties, additional amounts and additions to the tax, is not otherwise provided for, the Director may establish the same by regulations.

(c) The Director may, at any time within the period prescribed for assessment, make a supplemental assessment, subject to the provisions of § 521 of this title where applicable, whenever it is found that any assessment is imperfect or incomplete in any material respect.

68 Del. Laws, c. 187, § 1.