The archive function in LDDA is a manual process, you select the devices and right click and choose archive to asset control. Those devices are then sent to asset control and you can view them in there, asset control can does have query and reporting functionality.
The other way that devices can be missing from inventory is if they are deleted(this is a non DA function) This can either be a manual deletion or you can set up the inventory service to remove after x days(days to keep scans setting in the configure services inventory setting) if no scan has came in. By default this setting is set to 0 meaning we never remove devices.
Thanks Jason.. Where is the setting for the Inventory deletion. I thought it was set to 0 but with all these missing machines something's going on.