This issue is challenging, for a variety of reasons. Changes in the way stamps were numbered; color listings, and the skipping of numbers in the Scott system are some of the challenges. When the Continental Bank Note Company was requested to create the card proofs and special printings in 1875, they created new plates for the 1, 2, 5, 10, and 12 cent stamps. These are indistinguishable from the original plates as singles, but because of the wider spacing between the stamps can only be distinguished in pairs or blocks.
There are multiple colors for some of the denominations, resulting in multiple Scott numbers. However, not all colors were produced as proofs. This means some Scott numbers will not have a corresponding P4 proof.
Scott 64, 65, 66 and 74 are all major numbered stamps for the three cent issue; the difference is color. Scott 64 is pink; Scott 65 is rose (with many shades); Scott 66 is lake while Scott 74 is scarlet (both are only listed as a trial color, designated as such by the “TC”). Of these, only Scott 65 and Scott 74 have a corresponding P4 proof. Scott 66, the lake shade, is provided in this collection as an India proof (P3). Scott 67, Scott 75 and Scott 76 are all major numbered stamps for the five cent issue. Scott 67 is olive, Scott 75 is red brown and Scott 76 is brown. Only Scott 76 has a corresponding P4 proof. Scott 70 and 78 are both major numbered stamps for the twenty-four cent issues; they both have a P4 proof. There are two additional stamps which became part of this series. The two cent black, known as the “Black Jack” is added, as is the fifteen cent black, issued quickly, as a mourning stamp for President Lincoln. These both have P4 proofs. On top of this, certain colors were only printed in one printing and for those issued in all printings, there are shade variations.