Google Admin Portal does not allow devices to be deleted after it has been associated with an account. The only option is to "Deprovision" a device, which un-assigns a license from that device, but still remain in the account.

Currently, when the SMA performs a discovery, there is not a way to filter these "deprovisioned" devices that are discovered. All devices are discovered regardless of status. (Google API provides a method of filtering the devices being discovered.) Devices now have to be discovered and manually added. This is a VERY tedious task, as working for a school district, we will be deprovisioning 1000 Chrome devices each year as well as adding 1000 new devices. We cannot purchase 1000 new agentless device licenses each year.