One of the "charms" of the classic-era of US commemorative coins was the fact that coin sponsors typically had the authority to determine how many coins they wanted to order from the Mint (within the guidelines established by their coin's enabling legislation) and handled the marketing and distribution of the coins. Today, the Mint manages production, marketing and distribution of modern commemorative coins and simply sends a check (or checks) for the amount of earned surcharges to the sponsor once its sales figures are finalized and audited.
Many of the coins from the classic era did not sell out their entire mintage - their sponsor's were often overly optimistic. Often, the coin's sponsor returned thousands of unsold coins to the Mint to be melted. In many cases, the number of coins melted exceeded 50% of the number of coins struck!
Here are two "Top 5" Lists - one by total coins and one by percentage - of the "leading" melted classic-era commemorative coins:
Classic Era Commemorative Coins Melted: Top 5 By Total Count
# Year Coin Authorized Struck Melted Percentage
5. 1926 American Independence Sesquicentennial - Silver $0.50 1,000,000 1,000,000 859,408 85.94%
4. 1925 Stone Mountain Memorial 5,000,000 2,314,000 1,000,000 43.22%
3. 1951 George Washington Carver-Booker T. Washington 3,418,369 2,422,000 1,093,198 45.14%
2. 1946-51 Booker T. Washington Birthplace Memorial 5,000,000 3,166,000 1,581,631 49.96%
1. 1892-93 World's Columbian Exposition - Silver $0.50 5,000,000 4,050,000 2,501,700 61.77%
Classic Era Commemorative Coins Melted: Top 5 By Percentage
# Year Coin Authorized Struck Melted Percentage
5. 1926 American Independence Sesquicentennial - Gold $2.50 200,000 200,000 154,267 77.13%
4. 1921 Pilgrim Tercentenary (Total Authorization of 300K) 300,000 100,000 80,000 80.00%
3. 1926 American Independence Sesquicentennial - Silver $0.50 1,000,000 1,000,000 859,408 85.94%
2. 1903 Louisiana Purchase Exposition - Gold Dollar 250,000 250,000 215,250 86.10%
1. 1928 Oregon Trail Memorial (Total Authorization of 6.0M) 6,000,000 50,000 44,000 88.00%
Note: US Mint Reports and Hearings of Congress were used as sources for the above.