The Device Scanner does not perform real-time updates. For example, if you add a USB device to the computer after you perform a scan, the Device Scanner does not automatically detect it and update the scan data. To update a scan, you need to initiate a new scan.
Scans are additive, meaning that if you have data in the Device List, new devices are added to the scan data. However, old devices (those that are no longer present on the computer), are not removed; to remove a device from the list, you must manually delete it.