The 1878 proof three dollar gold piece boasts one of the lowest mintages of the series, with just 20 pieces struck. Walter Breen believed the issue was coined simply to fill out the gold proof sets for the year, and all of the sets were apparently sold. The elusive nature of the 1878 proofs was well known to 19th century numismatists, and W. Elliot Woodward called the date 'rare' in his catalog of the Heman Ely Collection in 1884, only six years after the set was issued. Experts believe only 10-12 examples are extant today in all grades.