Best I can tell is machine doubling which is not an error but the result of poor machine maintenance.
One of the better places to look for doubled die coins in this series in the recent past issues, is inside the main entrance along the side walls and above in the triangle above the main entrance. You can check these out at www.doubleddie.com.
I am sorry and in error about the link I posted to you. It should have been www.briansvarietycoins.com. Brian Ribar does nickels, John Wexler does not.