1878 Twenty-Cent Piece. Proof-64 (NGC). CAC. OH. Beautifully toned in rich steel-olive and pinkish-gray, sharp design elements and a mirrored finish provide further visual appeal. The popular and eagerly sought 1878 is a Proof-only issue from the final year of the twenty-cent series, the mintage just 600 coins. PCGS# 5306. NGC ID: 27H5. NGC Census: 12; 9.