Supposedly two or three proof $20 Liberties were struck in 1850. Today, only one survivor is known. It is in the collection of the Bibliothèque Nationale de France museum in Paris. It is a cleaned PR61. I have personally examined the coin and it is absolutely an unquestionable proof, it just sadly has been fairly harshly cleaned at some time in the past. The coin is part of the collection of a French national who came to the United States circa 1840, made his fortune, and returned to France. He was fortunately a coin collector who obtained many important coins directly from the U.S. Mint while he was in the United States.