The 1936 Landing of the Swedes in Delaware Tercentenary Half Dollar is often held up as an example of confusing dating in the classic-era series. The coin features a "1936" date on its obverse, was struck in 1937 and commemorates an event celebrating its 300th anniversary in 1938. One coin, three date connections!
(The 1936 Battle of Gettysburg 75th Anniversary Half Dollar is another example of a coin bearing a date ("1936") that was struck in 1937 and precedes the anniversary date (1938) being commemorated - its story parallels that of the Delaware.)
While the dating appears confusing on its surface, it's important to realize that it happened not for uninformed reasons, but because a sponsor was planning ahead and Congress was proactively attempting to prevent collectors from being abused/exploited.
Rather than wait until 1938 (or late 1937) to sponsor a coin bill in Congress and then push to rush its approval, the Delaware Swedish Tercentenary Commission planned ahead and acted in Q1 1936 with Joint Resolutions being introduced in the House of Representatives and Senate on its behalf. The Senate Resolution moved quickly through Congress, and was authorized by Congress and approved by US President Franklin Delano Roosevelt in March 1936 - more than two years ahead of the landing's 300th anniversary!
As a means of protecting collectors from a multi-date issue designed to exploit a collector's inherent "need" to collect complete sets, the Resolution included language that specified 1936 as the date that was to appear on the coins: "The coins herein authorized shall bear the date 1936, irrespective of the year in which they are minted or issued."
Such language enabled the Mint to strike the coins in 1937 and release them to their sponsor the same year - ahead of the 1938 commemoration events in Delaware.
(Note: the coin's reverse design features dual dates to mark the anniversary - 1638-1938.)1936 Landing of the Swedes in Delaware Half Dollar

So, two positive actions - proactive planning and consumer protection - created a scenario that some find confusing. Once the background facts are considered, however, the date confusion should fade away!
For other of my posts about commemorative coins and medals, including more about the Delaware half dollar, see:
Commems Collection.