On the 1968 dies there was an issue with a doubled working hub. So a lot of the listed ones on a few sites, have not noticed this yet. But this site noticed it.
Quote:
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.
Die Markers: The obverse and reverse die markers will vary with each affected working die.
Submitted By: Various individuals.
Cross References: None known
Comments: Numerous working dies for all three Mints were created with this doubled working hub including S-Mint proof dies.(underline added by coop)
Another issue with the coins from 1968-1972, they had a lot of
Machine Doubling present during that time. So may often think they have a doubled die, when it is really
Machine Doubling.