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.
Washington Quarter struck on a clad dime planchet. Full date!
1975 Lincoln Cent struck on a clad dime planchet.