31 C.F.R. § 500.549 Proof of origin.
Title 31 - Money and Finance: Treasury
Specific licenses for importation of goods the origin of which is North Korea, North Viet-Nam, Cambodia, or South Viet-Nam are generally not issued unless the applicant submits satisfactory documentary proof of the location of the goods outside North Korea, North Viet-Nam, Cambodia, or South Viet-Nam prior to the applicable effective date and of the absence of any interest of North Korea, North Viet-Nam, Cambodia, or South Viet-Nam in the goods at all times on or since that date. Since the type of documents which would constitute satisfactory proof varies depending upon the facts of the particular case, it is not possible to state in advance the type of documents required. However, it has been found that affidavits, statements, invoices, and other documents prepared by manufacturers, processors, sellers or shippers cannot be relied on and are therefore not by themselves accepted by the Office of Foreign Assets Control as satisfactory proof of origin. Independent corroborating documentary evidence, such as insurance documents, bills of lading, etc., may be accepted as satisfactory proof. [41 FR 16555, Apr. 20, 1976]
Title 31: Money and Finance: Treasury
PART 500—FOREIGN ASSETS CONTROL REGULATIONS
Subpart E—Licenses, Authorizations and Statements of Licensing Policy
§ 500.549 Proof of origin.

