Officials et al

General Issue Proprietary Stamps 1871-1919 – Part 1 (71MB)
General Issue Proprietary Stamps 1871-1919 – Part 2 (18MB)
General Issue Proprietary Stamps: 1871-1919 by William Gerlach, 230 pages.

Official Seals of US and Possessions (64MB)
Official Seals of US and Possessions by William Gerlach, 153 pages.

Official Mail of the U.S.P.O. 1778-1970 – Part 1 (41MB)
Official Mail of the U.S.P.O. 1778-1970 – Part 2 (30MB)
Official Mail of the U.S.P.O. 1778-1970. Fumiaki Wada. 128 pages.