Here's a case of "Don't believe everything you read!" And now, for your reading pleasure! 
The 1921 Missouri Statehood Centennial half dollar was struck to commemorate the 100th anniversary of Missouri joining the Union on August 10, 1821 - it was the 24th State to be admitted. To help celebrate the anniversary, the Missouri Statehood Centennial Exposition and State Fair was staged in Sedalia, MO August 8-20, 1921.
A total of 50,028 (28 for assay) Missouri Statehood Centennial half dollars were struck in Philadelphia in July 1921. This was in time to make them a part of the Centennial Exposition; the "Plain" variety available for sale at the Exposition. The coins were sold for $1.00 each, with the net proceeds helping to defray expenses associated with the Centennial celebration. (The "2*4" variety of the Missouri went on sale well after the Exposition closed.)
Knowing the coins were sold at a premium, I was surprised to see the following in the
Missouri Historical Review (Volume XV, October, 1920 -- July, 1921) in a piece about the Centennial Exposition and Fair:
"In commemoration of the occasion the United States mint will coin 250,000 Centennial Half-dollars bearing a special Centennial design. These coins are to be given out at the Exposition gates, as change for money paid for tickets."
Note: The law that authorized the Missouri half dollar did allow for up to 250,000 coins to be struck. However, only the original batch of 50,000 was ever struck - sales did not warrant additional production.To my knowledge, the Missouri half dollars were never distributed at face value by the Missouri Centennial Commission. The misunderstanding highlighted above can likely be attributed to a publishing deadline and the story about the Exposition being written before plans for it were finalized. You can't always believe what you read (or hear)!
1921 Missouri Statehood Centennial Half Dollar, Plain Variety
1921 Missouri Statehood Centennial Exposition and State Fair Program, Cover
For other of my posts about commemorative coins and medals, including more on the history of the Missouri Statehood half dollar and its two varieties, see:
Commems Collection.