(a)

(1) For the sole purpose of determining the net taxable estate under this part and part 4 of this chapter, there shall be allowed against the net estate a maximum single exemption against that portion of the estate distributable to one (1) or more beneficiaries of Class A of an amount determined according to the following schedule:and there shall be allowed against the net estate a maximum single exemption against that portion of the estate distributable to one (1) or more beneficiaries of Class B of an amount determined according to the following schedule:

before January 1, 1984

before January 1, 1985

(2) After 1989, no distinction shall be made in classes of beneficiaries and all beneficiaries listed in subsection (b) in Class B shall be included in Class A.

(b) For the sole purpose of determining the net taxable estate under this part and part 4 of this chapter, there shall be allowed against the net estate a maximum single exemption against that portion of the estate distributable to one (1) or more beneficiaries of an amount to be determined by the following schedule:

before January 1, 1999

(c) In the case of estates of nonresidents, the exemptions in this section shall be apportioned in the ratio that the value of the property included in the gross estate; to wit, property, the transfer of which is subject to the tax imposed bears to the value of all of the property that would have been included in the gross estate, if the decedent had been a resident of this state; provided, that, in any event, such proportionate part of the exemption shall not be less than is permitted by the Constitution of the United States.