(a) Mail articles for copyright. Mail articles marked for copyright which are addressed to the Library of Congress, to the U.S. Copyright Office, or to the office of the Register of Copyrights, Washington, DC, shall be passed free of duty without issuing an entry.

(b) Books, engravings, and other articles. Books, classifiable under subheading 4903.00.00, Harmonized Tariff Schedule of the United States (HTSUS) (19 U.S.C. 1202), and engravings, etchings, and other articles enumerated in subheading 9808.00.10, HTSUS, shall be passed free of duty without issuing an entry when they are addressed to the Library of Congress or any department or agency of the U.S. Government.

(c) Official Government documents. Other mail articles addressed to offices or officials of the U.S. Government, believed to contain only official documents, shall be passed free of duty without issuing an entry. Such mail articles, when believed to contain merchandise, shall be treated in the same manner as other mail articles of merchandise so addressed.