Ron Guth: Following unsatisfactory results with the coining of the Type Two Gold Dollars, further modifications to the designs were deemed necessary. Liberty's head was enlarged, her hair was arranged differently, and the headress was shifted toward a more horizontal plane. The purpose of these changes was to minimize the number of places where recessed areas in the dies opposed each other, allowing metal to flow into the dies more evenly and allowing the coins to become "fully struck." In general, the changes were successful, although quality control at some of the branch mints (notably, Dahlonega) resulted in poorly made coins with less-than-optimal striking qualities.
A survey of the dates in this series show two years (1856 and 1862) with massive mintages (approaching two million pieces in the case of the 1856). This contrasts with other years, where production was trivial: in 1875, only 400 gold dollars were produced; many other years have mintages in a 3,000-5,000 coin range. The rarest and most desirable dates in this series are the 1856-D and 1861-D, both of which are innately rare and especially difficult to locate in Mint State.
For type collectors, high grade examples are readily available. At the extreme high end, PCGS has certified two MS-69 examples, one from 1864 and another from 1880.