The Inner Join you posted works well but I have some PCs that have not sent inventory. They are in the stock room but has been imported via the connector off of a spreadsheet. They are in NS (ns 7) only as a serial number (and of course has a GUID).
Basically, I would see PCs (in this case serial numbers) not in the Evt_AeX_Client_LogOn table as well as PCs with all the event logon stuff that you already posted about.
DECLARE @v1_TrusteeScope nvarchar(max)
SET @v1_TrusteeScope = N'%TrusteeScope%'
SELECT
[vri2_Computer].[Guid] AS [_ItemGuid],
[vri2_Computer].[Name] AS 'PC Name',
[dca5_AeX AC Identification].[Hardware Serial Number] AS 'Serial Number',
[dca5_AeX AC Identification].[Client Date] as 'Last Contact',
va.[Status],
[dca6_AeX AC Primary User].[User] AS 'Primary User',
[dca3_AeX Client LogOn].[User] AS 'Last LogOn-Off User',
ugd.[Display Name] AS 'Display Name of Last User',
[dca3_AeX Client LogOn].[Event],
[dca3_AeX Client LogOn].[Time] AS 'Event Time',
aci.[Location],
[dca4_HW Logical Device].[Model],
FROM
[vRM_Computer_Item] AS [vri2_Computer]
LEFT OUTER JOIN [Evt_AeX_Client_LogOn] AS [dca3_AeX Client LogOn]
ON ([vri2_Computer].[Guid] = [dca3_AeX Client LogOn].[_ResourceGuid])
LEFT OUTER JOIN [Inv_HW_Logical_Device] AS [dca4_HW Logical Device]
ON ([vri2_Computer].[Guid] = [dca4_HW Logical Device].[_ResourceGuid])
LEFT OUTER JOIN [Inv_AeX_AC_Identification] AS [dca5_AeX AC Identification]
ON ([vri2_Computer].[Guid] = [dca5_AeX AC Identification].[_ResourceGuid])
LEFT OUTER JOIN [Inv_AeX_AC_Primary_User] AS [dca6_AeX AC Primary User]
ON ([vri2_Computer].[Guid] = [dca6_AeX AC Primary User].[_ResourceGuid])
LEFT JOIN dbo.vAsset va
ON va.[_ResourceGuid] = [vri2_Computer].[Guid]
LEFT JOIN dbo.vAllComputerInfo aci
ON aci.Guid = va._ResourceGuid
LEFT JOIN dbo.Inv_Global_Windows_Users gwu
ON [dca3_AeX Client LogOn].[User] = gwu.UserId
LEFT JOIN dbo.Inv_Global_User_General_Details ugd
ON ugd._ResourceGuid = gwu._ResourceGuid
INNER JOIN (SELECT max(_id) as MaxID, _ResourceGuid FROM [Evt_AeX_Client_LogOn] GROUP BY _ResourceGuid) AS grouped_cl ON [dca3_AeX Client LogOn]._ResourceGuid=grouped_cl._ResourceGuid AND [dca3_AeX Client LogOn]._id=grouped_cl.MaxID
WHERE
(
(
([dca4_HW Logical Device].[Description] = N'AT/AT Compatible')
)
AND DATEDIFF(hh, [dca5_AeX AC Identification].[Client Date], getDate()) > '120'
AND [dca4_HW Logical Device].[Model] NOT LIKE 'HP%'
AND [dca4_HW Logical Device].[Model] NOT LIKE 'Latitude%'
AND [dca4_HW Logical Device].[Model] NOT LIKE 'Inspiron%'
AND [dca4_HW Logical Device].[Model] NOT LIKE 'Power%'
AND [dca4_HW Logical Device].[Model] NOT LIKE 'Optiplex 170L'
AND [dca4_HW Logical Device].[Model] NOT LIKE 'VMWare%'
--AND
--([vri2_Computer].[Guid] IN (SELECT [ResourceGuid] FROM [ScopeMembership] WHERE [ScopeCollectionGuid] IN (SELECT [ScopeCollectionGuid] FROM dbo.fnGetTrusteeScopeCollections(@v1_TrusteeScope))))
)
ORDER BY
--aci.[Location],
--[dca5_AeX AC Identification].[Client Date] DESC
[Serial Number]