Inverted design error?

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My eyes must be playing tricks on me because I can't find this error listed in Charlton.

Would this be called an inverted design error?  I can't believe a note like this just accidentally made it out the door with such an obvious mistake.  But more than that, it actually circulated and grades Fine with pinholes.  Since I'm not an error collector, I'd like an opinion of what this would be worth.

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Nice find M.
It's listed on page 409 section E27 inverted design, values range 6,500 to 2,500 and less depending on grade and desirability which I think might be pretty good.