This is going to return quite a few rows but will give us an idea of when machines have last run their Inventory policies. If you have cloned your Inventory policies, then you will need to change the GUIDs I use. If a machine has never run Inventory, it will not appear in this list...and that will need to be researched. Hope this helps some...:)
SELECT ci.Name, i.Name, ti.StartTime, ti.EndTime, ti.InstanceStatus, ti.Result, ti.Success
FROM vRM_Computer_Item ci
JOIN Evt_Task_Instances ti
ON ti._ResourceGuid = ci.Guid
JOIN ItemVersions iv
ON iv.VersionGuid = ti.TaskVersionGuid
JOIN Item i
ON i.Guid = iv.ItemGuid
WHERE ParentTaskInstanceGuid IN ('8918C4B8-F6D0-45C3-BCB9-4628D264DA20', '2ac2b64e-a58a-41b0-a6ca-7994bdede5c4', '225067fa-37b3-4b3a-af01-a9c37bb553d6') -- Inventory Tasks
ORDER BY ti.EndTime