Many types of mint errors are missed by inspectors and are inadvertently released into circulation. Clipped Planchets, Off-Center Strikes, and Wrong Planchets are just a few examples of the many types of error coins that slip out of the mint occasionally. Some errors are fairly common, but many are extremely rare.
1956 Franklin Half Struck on Silver 25c Planchet. A brilliant example that was mistakenly struck on a 25c planchet. Devices are very well centered except the very top of Franklin's head and the very bottom of the bell's clapper have both been cropped. The full date is completely rendered and partial lettering along the periphery is still evident.