Note on Wexler's site, there was an issue with a doubled working hub. That hub created many dies that were used from different mints. So they are common. He does list a few that are doubled dies below this listing. http://doubleddie.com/814660.html
1968-P,D,S 1˘ WWHO-001 Doubled Working Hub
Description: A very slight CW spread shows on the LIBE of LIBERTY. A spread towards the rim shows on IGWT.