(1) Any tax levied by authority of this part shall not apply to any sand, gravel, sandstone, chert and limestone severed to meet the obligations of any written contract for sale of the product entered into prior to June 5, 1984.
(2) Any sand, gravel, sandstone, chert or limestone that has been severed and on which any severance tax has accrued prior to June 5, 1984, in the county in which the severance has occurred shall be exempt from this part, if such tax has been paid.