Sadly this type of stuff has to be audited. Sometimes you can sort by name and see if there is a duplicate or similar name indicating that a device may have been replaced. Otherwise, you may have to reconcile against outgoing employees to see if devices have been retired or removed. It's one of those things that is easier to keep up on than it is to go back and figure out each one. We deal with this same issue for our managed AV.
Adam R MS | CISSP, CISM, VCP, MCITP, CCNP, ITILv3, CMNO
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