Wonderful coin designed by the grande damme
Laura Gardin Fraser. Really like your example.

This coin is one of the four holes in my type set.
Struck in October 1921, this variety also employed the gimmick I mentioned about your Missouri Half ... in this case the 2x2 as shown on your coin. Interesting fact is that the "x" is actually the St. Andrew's cross ... taken from the Alabama state flag ... the design which inspired the Confederate flag.

Authorized in 1920 and struck in 1921 to commemorate an event that occurred in 1919, this coins contains a confusing array of three dates.
Thanks for sharing your 2x2 example.
David
Take a look at my other hobby ...
http://www.jk-dk.art