Dang, why didn't someone notice?

Artnet News

A Startling Discovery: A Painting Had Been Hung Upside-Down for 75 Years!

....Flipping the composition would mean that the tight grouping of lines traditionally found at the bottom was really meant to be at the top—matching the orientation of a very similar work, New York City (1942), held at the Centre Pompidou in Paris....

The curator considers the wrong hanging to be just part of its long history. “Perhaps there is no right or wrong alignment at all?” she suggested to Germany’s Monopol Magazin.

See also Call it "art."