A museum’s empty space can belong to something that was never returned.

A gap in a display can be an argument. Something was taken, or bought under conditions that would not be accepted now, and the empty case marks a claim rather than an absence. Museums are not neutral warehouses, they are the outcome of who had the power to collect, and the vacancies are part of that record.

When you see a gap or a note about provenance, read it as history rather than housekeeping. Ask where an object came from before admiring it. The question is not hostile and it is usually the more interesting story.