Major mint errors on U.S. gold coins are very rare. This is only one of two major mint errors on a gold coin from the U.S. Branch Mint in Carson City, Nevada that I am aware of. A slightly double struck Carson City Morgan Dollar recently sold for approximately $30,000. There are many serious collectors who place special importance on mint errors from the Carson City Mint due to its history.
This Carson City $20 Liberty has a full partial collar which is easily seen in the new NGC holder which displays the edge. This date is also rare and in this condition is a five figure coin, even without the partial collar. This Carson City $20 Liberty is a recent discovery and is very exciting since it combines the rarity of a major mint error on a gold coin with the popularity and history of the U.S. Branch Mint in Carson City.