When Germany was reunified, the Ethnological Museum was reunified too. But like the rest of the country, the reintegration of its collection was an uneven process. That has left some curators not entirely certain of what they have.

There are many reasons for that. Some returned objects were incorrectly identified, like a group of West African ancestral figures that were mistaken for tools, said Jonathan Fine, a curator in the Africa collection.

Roughly 2,000 of the returned objects could not be identified because they lost tags or had been damaged, Professor Koch said. They have sat for years in storage in over 100 boxes.

Museum officials said they were digitizing their entire collection to build an online database as part of the restitution guidelines adopted earlier this year. As objects are digitized, they will also be cleansed of toxic dust. But that work is going slowly.

Mr. Della, the postcolonial activist, said accounts of damaged objects and confusion in the depots called into question the museum’s ability to repatriate artifacts if their original countries ask for their return.

“If Germany is serious about returning objects to their original countries it has to take care of them and have them in some order,” he said. “An object that has been lost or destroyed cannot be returned.”