Estimated grade. Sold in Stack's Auction of Garrett / Hopkins University, Mar. 1976
The Proof-only 1875 $3 is, indeed, one of the great gold rarities of the nineteenth century. Clearly, the mintage figure of 20 Proofs is incorrect (or at best, low) because more than 20 examples are known to exist. Brene claimed to know of 31 different examples. We know of sixteen demonstrably different examples and we have yet to examine and exhaust the complete auction history. Whether the additional examples were struck later in 1875 or in later years is unknown, though the presence of die rust on some of the examples suggests a later restriking. In reality, the question is academic because these 1875 Proofs are hotly contested whenever they appear at auction. They are the only way to own an 1875 $3. Today's auction results are somewhat higher than the ones recorded by Akers -- three different examples have sold for over $200,000 each, and two have sold for $253,000 each.
Where non-Cameo, Cameo, and Deep Cameo examples were once lumped together by PCGS, they are now beginning to separate and it appears that most examples are Cameo at a minimum.