1851 - Toppan, Carpenter, Casilear & Co add an imprint to their plates.

May 10, 1861 -  Postmaster General Blair awards a contract to National Bank Note Company, who started putting their imprint on plates.

1873 -  Continental Bank Note Co. is awarded the contract to print stamps.  The National plates, dies and transfer rolls were turned over to Continental, who made new plates of the lower denominations.

December 1878 -  National, Continental, and American bank note companies are consolidated into the American Bank Note Company.

February 1879 - The stamp contract held by Continental is assumed by American Bank Note.

May 1906 - Siderographer Charles Vermeule (C.V.) initials plate #3080.

1908 - Plate Finisher John Reding (J.R.) initials plate 4959 (335 and 347).

1909 -  Stars (¶-open and «- solid) are added to the BEP imprint to indicate variations in separation between stamps.

1910 -  The letter A is added to the BEP imprint to indicate uniform spacing of 2¾ mm between stamps.

December 31, 1915 -  The first experimental plates marked S20 go to press.  They are followed later by plates marked S40, S30.

May 14, 1918 - William T. Robey purchases “Inverted Jenny” pane of 100 (C3a).

May 15, 1918 -  Plates for bi-color stamps are marked TOP to reduce of the possibility of a sheet being inverted on its second pass through the press.

May 9, 1919 - The letter F is added to the selvage to identify an approved hardened plate.

May 1920 - Otto A. Myers inscribes his monogram in the margin of plate 11329.

1928 - Siderographers/Plate Finishers instructed to stop putting initials on the front of plates.

February 12, 1933 - Georgia Bicentennial Issue released with C.S. marking indicating that the plate had been chromium plated.

1933 - Electric Eye margin line and dashes experimentally used.

1935 – First Electric Eye plates made for 2¢ Washington (634).

April 1938 - Electrolytic plates for 6¢ Airmail issue (C23) marked EI (electrolytic iron).

1939 - Electric Eye frame bars and gutter bars first used.

November 23, 1962 - Booklet pane 1213a is issued with a label stating “YOUR MAILMAN DESERVES YOUR HELP KEEP HARMFUL OBJECTS OUT OF YOUR LETTERS.”

May 5, 1964 - Battle of the Wilderness (1181) issued with Mr. Zip and “Use Zip Code” insignia.

January 29, 1966 - 6¢ FDR (1284) issued (only on Bureau precancels) with “Mail Early in the Day” and “Use Zip Codes”.  The Surrender at Saratoga American Bicentennial Issue (1728) was the last stamp issued with a “Mail Early” slogan.

1977 - USPS Philatelic Release No. 57 announces that the designs of all postage stamps and postal stationary items would be copyrighted.

January 11, 1978 - The Indian Head Penny issue (1734) issued with a registered slogan.

September 23, 1978 - John Paul Jones US Bicentennial (1789) issued with a copyright notice.

1986 - USPS abruptly retires Mr. Zip after 22 years of dedicated service.  Stamps with Zip slogans continue to be issued until 1994 .

February 18, 1990 - USPS prints biographical information [“Luis Munoz Marin (1898-1980.  First elected Governor of Puerto Rico, 1948.  Founder of Puerto Commonwealth.”] in the selvage of Scott 2173, the first stamp in the Great Americans series to contain such information.

July 24, 1992 - The Wildflowers (2647-2696) pane of 50 issued with a diagram which identifies position, shaded in grey, on a sheet from which the pane was cut.

January 21, 1994 - The Edward R. Murrow (2812) commemorative is released with the calculation of the price of the pane in the margin. 

July 29, 1998 - Breast Cancer Awareness semipostal (B1) is issued with bar codes and item number in the margin.

March 16, 2001 - Diabetes Awareness stamp (3503) is issued with a web site in the margin.