Reply to post:

Here is an idea: garbage collection of containers. Randomly shutdown (do not remove the data, for at least one year) containers which have not been monitored by appropriate application monitoring tool for extended period of time, then wait until someone starts complaining. Of course, some application monitoring needs to be in place, so if your organization is only monitoring the infrastructure but not the applications, that is not enough to instantiate such policy (and also part of the reason why you might not know what-the-hell-is-that-thing-doing)