Each Government agency shall retain the original of its permit, Form 5150.33, on file. When filing an initial customs entry to withdraw spirits free of tax from a port of entry, the agency shall furnish a photocopy of its permit to the district director of customs for retention. In the case of an agency holding a single permit for use of its sub-agencies, an attachment to the permit shall list all locations authorized to withdraw spirits free of tax from customs custody. Any subsequent requests for customs entry from the same port shall refer to the permit number. (Sec. 201, Pub. L. 85-859, 72 Stat. 1375, as amended (26 U.S.C. 5313))