I found a "fuzzy" picture with a similar ink-gap in a very close proximity. Here is the link and what I see.
http://1.bp.blogspot.com/-fW8Exw-_ud...0/scan0019.jpg
On the left of the picture I transposed the position of this "mark" compared to yours. Close but not exact. I will keep looking.
If you have a more detailed scan of your card I would be happy to investigate more.