The year 1935 witnessed a unique scenario in the annals of the US classic commemorative coin series. It was in that year that six versions of the same coin were issued by a sponsor. I refer to the Daniel Boone Bicentennial Commission and its Daniel Boone Birth Bicentennial half dollar.
Early in the year, the Mint produced 1935-dated coins at Philadelphia, as well as in Denver and San Francisco (i.e., a three-coin P/D/S set). When it did so, the Boone bicentennial year (1934) was removed from the coin as it was no longer applicable (the Mint generally includes only the "struck" year on the coins it produces, unless otherwise directed). This did not sit well with the Bicentennial Commission. It asked the Mint to incorporate "1934" in the design for all future strikings, but was told by the Mint that such could not be done unless so authorized by Congress.
So, the Bicentennial Commission went back to Congress and successfully secured an amendment to its original legislation that mandated a 1934 date be included as a supplemental date on all future Boone coins. As a result, another batch of 1935-dated Boone half dollars was struck, but with a small "1934" added to the reverse to identify the bicentennial year of Boone's birth. (You can read the details of this scenario here:
The Small "1934" Boone Half Dollars.)
As was the case for the original 1935 issue, the "Small 1934" variety of the coin was struck at Philadelphia, Denver and San Francisco (i.e. a second three-coin P/D/S set). This made for
six versions of the 1935 coin being marketed to collectors! No other classic-era coin had six different versions of the same design type released in the same year.
Frank C. Dunn, a member of the Bicentennial Commission as well as a coin dealer, manipulated the market for the coins. First, claiming they were scarce/rare, he raised the Commission's issue price on the 1935/34 Denver and San Francisco coins to $3.70 for the pair (vs. $3.00 for the regular 1935 pair). He then claimed the "Small 1934" D and S coins were over-subscribed and refunded most orders. What angered collectors (and eventually Congress), however, was the fact that Dunn and other dealers suddenly had 1935/34 D-S sets available for $60.00 and up. Can you say "Collector Exploitation"?
1935/34 Daniel Boone Birth Bicentennial Half Dollar

For other of my posts about commemorative coins and medals, including more on the history of the Boone half dollar, see:
Commems Collection.