We use WMI Remote Registry to query remote workstations. If for some reason both of these protocols are not available due to not running, Firewall etc, then the report will mostly contain information returned by Active Directory.
To get a better assessment, you should consider possibly going to each (unreachable) machine with the Local Data Collector to get more detailed information that could not be retrieved remotely.
You can also use Group Policy to assist in opening these protocols.
