On exportation of metal pursuant to the provisions of section 312(b)(1), Tariff Act of 1930, as amended, the general procedure covering warehouse withdrawals for exportation shall be followed. The proprietor of the plant from which the withdrawal is made shall prepare a sufficient number of copies of withdrawals on Customs Form 7512, in addition to any other copies required by the regulations, to enable the director of the port of withdrawal to forward a copy to the director of each other port where credit is to be applied. Such withdrawals shall designate the plant or plants which are to receive the credit, shall specify the warehouse entry number or numbers to which the credit is to be applied, and shall state the quantity of dutiable metal which is to be applied to each warehouse entry specified, and when any of the credits specified represent the last withdrawal against a particular warehouse entry, the words “final withdrawal” shall be shown on the withdrawal. When two or more plants nearest a given port are designated to receive credit, sufficient copies of the withdrawals shall be prepared to cover each such plant and entry. If at the time of withdrawal the warehouse proprietor does not know the plants or warehouse entry numbers which are to be credited with the withdrawal, or the metallic content of the dutiable metal being exported, the preparation of the before-mentioned copies of Customs Form 7512 may be postponed for a period of not longer than 30 days from the date of the movement of the dutiable metal from the plant. In such cases, a so-called memorandum withdrawal, in the number of copies provided for in § 144.37 of this chapter, may be used in the first instance for the purpose of obtaining the required Customs record of the exportation of the dutiable metal under Customs supervision. All memorandum withdrawals shall be conspicuously endorsed “Memorandum Withdrawal.”