Incompleteness 
As I heard the story of the Carson City Mint, it started life as a private operation, because the US Treasury refused to build a branch to accommodate the Comstock Lode.  When the government attempted to close it down and prosecute the operators for counterfeiting, the prosecution was defeated by the detail that the dollar coins were fractionally overweight.  The street price of silver in Carson City was low enough to still permit a profit on the minting. Thus, unable to prevent the minting of silver coins in Carson City, the Treasury took over operations and pocketed the fractional overweight.  Even if this story is inaccurate, I believe the story ought to be included, perhaps with its disproof, but it does shed light on the issue of the discrepancy between the value of silver as a commodity and as currency.