Every year that the Philadelphia Mint produced business strike Gold Dollars of the Type III design, it also delivered proofs.  In keeping with the standards of the U.S. proof gold series as a whole, all specimen deliveries in the Type III Gold Dollar series are rare.  The earliest issues are the most elusive, the 1856, 1857 and 1858 having unknown, although presumably very limited original mintages.  The late-date deliveries, particularly those struck during from 1882 through 1889, are usually encounterd with more frequency in today's market.  Due to limited business strike mintages during the 1880s, however, the proofs from that decade are eagerly sought by date collectors.  The proof Gold Dollars from the 1860s and 1870s are underrated and, as a rule, much rarer than their original mintages (many of which are already limited) might suggest.