> the museum never even knew they’d had them to go missingThis is increasingly a problem for museums and libraries all over the world. They keep accreting material but their exhibit space is often shrinking, or badly maintained. Security is mostly an afterthought, ungodly amounts of precious artefacts disappear without people realizing for years. This is particularly bad in Europe, where museums are centuries old at this point and often overflow with material.
The solution is probably to somehow link artefacts to RFID tags or similar, or enclose them in boxes with such features, which can be monitored automatically. It's obviously a challenge (you can't just place a sticker on the Gioconda, but if you make it too easy to non-destructively remove it, it's self-defeating; and they already take years to just build their inventories, let alone secure each individual item).