Usually if it's a print flaw it's pretty easy to find other examples but I couldn't find any. If you're sure it's not paper loss or a small piece of excess paper stuck on the card I would keep it and see if any other examples pop up.
Here's a Gilbert I picked up recently that is missing part of the G.
img685.jpg
When I got it I could tell it was a print flaw and in a short search I found it on 3 other backs.
Old Mill 1.jpg
PD350-1.jpg
SC350-30-1.jpg