Apparently spurred on by the ease with which blood flowed during the Civil War, a religious revival swept through much of the United States in the 1860s. This revival touched the Seated Dollar in 1866 through the addition of the motto IN GOD WE TRUST to the reverse design. The first proofs of this new type were struck that year, as they would be every year through the series' end in 1873.
There is little difference between the rarity of the eight proof deliveries in the Motto Seated Dollar series. Nevertheless, some of these issues are more popular with collectors than others due to the rare, conditionally challenging nature of their identically dated business strike counterparts. Excellent examples are the 1866, (particularly) 1867, 1868 and 1869, which enjoy greater demand among date collectors than the 1870, 1871, 1872 and 1873. On the other hand, the final four issues are perhaps a bit more desirable with proof type collectors.