NPR offers an explanation for how a Picasso work disappeared into the Evansville Art Museum’s collection without anyone being aware of its presence:

 Curator Mary Bower says the work went unnoticed because of a clerical error.

“All the documentation associated with the gift indicated that this was by an artist named Gemmaux,” she says, “which really happens to be the plural of the artistic technique.”

That technique, gemmail, uses layered glass to create 3-D art. The work remained miscataloged for more than 40 years, until Bower got a call from Guernsey’s auction house in New York. They were doing research on the special glass technique Picasso used and had tracked one of the works to Evansville.

“I thought, ‘Yes, I do need to check in on that,’ ” Bower says.

For Museum, Long-Lost Picasso Is Too Costly To Keep (NPR)