Accounting segregation permits inventory based origin attribution subject to accepted accounting principles and customs verification. Where identical and interchangeable originating and non originating materials are used in manufacture, physical segregation by origin is required; however, producers facing significant cost or material difficulty may use an accounting segregation method. That method must be recorded and applied in accordance with the applicable Generally Accepted Accounting Principles, allow clear distinction between originating and non originating materials, guarantee that no more products receive originating status than under physical segregation over the accounting period, and be supported by inventory records for customs verification. Competent authorities may require prior authorisation.