Whenever the processing tax first takes effect, there shall be levied, assessed, and collected a tax to be paid by such person equivalent to the amount of the processing tax which would be payable with respect to the commodity from which processed if the processing had occurred on such date. Such tax upon articles imported prior to, but in customs custody or control on, the effective date, shall be paid prior to release therefrom. In the case of sugar, the tax on floor stocks, except the retail stocks of persons engaged in retail trade, shall be paid for the month in which the stocks are sold, or used in the manufacture of other articles, under rules and regulations prescribed by the Commissioner of Internal Revenue with the approval of the Secretary of the Treasury.

Whenever the processing tax is wholly terminated, (A) there shall be refunded or credited in the case of a person holding such stocks with respect to which a tax under this chapter has been paid, or (B) there shall be credited or abated in the case of a person holding such stocks with respect to which a tax under this chapter is payable, where such person is the processor liable for the payment of such tax, or (C) there shall be refunded or credited (but not before the tax has been paid) in the case of a person holding such stocks with respect to which a tax under this chapter is payable, where such person is not the processor liable for the payment of such tax, a sum in an amount equivalent to the processing tax which would have been payable with respect to the commodity from which processed if the processing had occurred on such date: Provided, That in the case of any commodity with respect to which there was any increase, effective prior to June 1, 1934, in the rate of the processing tax, no such refund, credit, or abatement, shall be in an amount which exceeds the equivalent of the initial rate of the processing tax in effect with respect to such commodity.