van Dam NFR15 EFO Offset on $100 KEVII,  mounted to card, Newfoundland, Canada
NOTE:  the "Newfoundland Specialized Stamp Catalogue" lists this Offset as R15c as being under the gum.  Now, looking at this stamp closely, you can see that the obverse has been cancelled.  Therefore, someone has used this stamp, as there is no longer any gum.  Very interesting item and still a tough error to get.  NSSC lists this at a value of $380 USD for Used (approx $475 CDN) .  I will leave affixed to card and purchaser can decide to soak or not.