Sure, inventory is unaccounted for but you as an engineer knows it's not accounted for. So you go to IT, and you ask for a new one. IT revokes access of the original key, and gives you a new one.

No one in that transaction cares if it was lost or stolen.

But it’s not enough to steal a blank YubiKey from the office storage room. You would have to steal some specific person’s activated YubiKey, and that person will notice it if they need the key regularly to do their job.