On October 19, a U.S. Air Force transport plane crashed as it was trying to land at Shindad Air Base in Afghanistan. Aboard was 4,700 pounds of mail meant for U.S. troops. The military has contacted every election administration office in the U.S. and explained that any absentee overseas ballot sent recently to zip code 09382 should be replaced. See this story. Zip code 09382 is one of the U.S. military zip codes, sent to state “AE” (Armed Forces Africa Canada Europe).
Mail absentee ballots always require that the voter sign the outer return envelope, which will protect against any duplicate ballots being voted on by any particular voter. Thanks to Bill Van Allen for the link.