I have been thinking about it for a while and have to post now since my fears came true. i upgraded our infrastructure a while ago including all the licenses as well. it is now that i realized that someone accessed the old (upgraded now) inventory of vsphere licenses and applied to few hosts. Since vsphere client have no way of telling if the key has been upgraded, we have been using a non-existent key for at least 4 months now. Is there a way to make sure to avoid this issue or if manually validating the license keys every once a while is the only solution.