(a) The tax imposed upon the value of the net taxable estate of a decedent, distributable in accordance with the classification, deductions, allowances and exemptions set out in this part shall be, respectively, at the following rates:
(1) Class A
(2) Class B
(b) In the case of a decedent dying in 2016, or in any subsequent year, no tax shall be imposed pursuant to this part; provided, however, that this subsection (b) shall not be construed to absolve liability for any tax duly levied by this section, during any year prior to January 1, 2016.