Quantity issued:
Estimates are based on available information, primarily from Brookman, "The United States Postage Stamps of the 19th Century- Volume I", "Linn's U.S. Stamp Facts 19th Century", published by Linn's Stamp News and Chase's "The Three Cent Stamp of the United States 1851-1857- Revised". These numbers are simply estimates based on the best information available and are subject to revision.

The 3¢ imperforate quantity issued is based on an estimated 360,000,000 stamps printed, with the vast majority being from the later plates. The best way to determine whether a stamp is an early, Scott 10 and 10A, or later printing, Scott 11 or 11A, is to determine which plate it was printed on. While it is true that most of the earlier printings are a shade of orange brown, it is not the color that determines the variety, it is the plate. The early printings were printed on plate 0, the early and intermediate plate 1 and the early plates of plates 2 and 5. The later variety was printed on the late plates of plates 1, 2 and 5, as well as plates 3, 4, 6, 7 and 8. In general, the early printings are much sharper than the later printings.

Design Size on the 1¢, 5¢ and 10¢ Stamps: All varieties other than type I have been at least partially cut away, sometimes on all four sides and to varying degrees within a particular type depending on plate position. This was done to make the design fit within the allocated space on the plate leaving adequate margins for separation. This was particularly true when adding perforations to the finished sheets became standard practice in 1857. Since the design width and height varied from stamp to stamp, even within a particular type, design measurements for the various types are meaningless.

Special Printings: The following information applies to all of the 1851 reprints. The Special Printings were issued to showcase a complete set of the U.S. issues for the first World's Fair officially held in the U.S., at the Centennial International Exposition of 1876 in Philadelphia and also to provide stamps for collectors and others to satisfy numerous requests. While "Reissued" stamps were valid for postage, "reprints" were not, since the series was demonetized in 1861. All of the 1851 reprints are easily identifiable by their gauge 12 perforations versus the gauge 15 of the regularly issued stamps.

Bibliography and suggested additional reading:
The Postage Stamps of the 19th Century, Volume 1, by Lester Brookman (1966)
The 1851 Issue of United States Stamps, Sesquicentennial Retrospective Hubert Skinner, Charles Peterson editors (USPCS 2006)
The 2011 Scott Specialized Catalogue of United States Stamps & Covers, Scott Publishing Co. 2010
United States Letter Rates to Foreign Destinations 1847 to GPU-UPU, by Charles J. Starnes
The United States One Cent Stamp of 1851-1857, by Stanley Ashbrook 2 volumes (1938)
The United States One Cent Stamp of 1851-1861, by Mortimer Neinken (1972)
The Three Cent Stamp of the United States 1851-1857 Issue, by Dr. Carroll Chase (Quarterman Reprint 1975)
The United States 3c Issue of 1851-1861: A Progress Report, by T. J. Alexander (39th Am. Philatelic Congress 1973)
The U.S. Five Cent Stamp of 1856: The Frederick R. Mayer Collection, by Richard C. Frajola & Frederick R. Mayer (2005)
The United States 5c Stamps of 1856-1861, by Henry Hill
The United States Ten Cent Stamp of 1855-1857, by Stanley Ashbrook (1936)
The United States Ten Cent Stamp of 1855-1859, by Mortimer Neinken (1960)
United States Twelve Cent Stamp of 1851-1857, by Stanley Ashbrook (1926)
The United States Twelve Cent Stamp of 1851-1857, by Mortimer Neinken (1964)
Plate Varieties of the United States Twenty-four Cent 1860, by Elliott Perry (17th Am. Philatelic Congress 1951)
The United States Ninety Cent Stamp of 1860 On and Off Cover, by S. Ashbrook (17th Am. Philatelic Congress 1951)

Design dimensions:
The Postage Stamps of the United States, John Luff (1902 and 1937)

Colors:
The Encyclopedia of the Colors of United States Postage Stamps - Volume 1 Issues of 1847-1868, by Roy H. White (1981)

Postal History:
United States Letter Rates to Foreign Destinations 1847 to GPU-UPU, by Charles J. Starnes
The U.S. Five Cent Stamp of 1856: The Frederick R. Mayer Collection, by Richard C. Frajola & Frederick R. Mayer (2005)
History of Letter Post Communication between the United States and Europe, by George E. Hargest

Plating:
Notes on the plating of the 10¢ stamp were published by Elliott Perry in the Collector's Club Philatelist from 1924-1926. Perry's plating of this stamp is considered one of the great milestones in the hobby.