With escalated events that contain values within the trigger name it gets substituted to UNKNOWN when the value is removed from the history tables.

For example we have 18 days history data (good) :

Host: eXXXXXXXX
Trigger: File System Capacity 94.88 % Used (D:\ [Data] (499GB NTFS)) [Critical]
Timestamp: 2016.06.07 07:00:15
Event ID: 35916542
Event Age: 16d 0h 1m

For example we have 18 days history data (bad):

Host: eXXXXXXXX
Trigger: File System Capacity UNKNOWN Used (D:\ [Data] (499GB NTFS)) [Critical]
Timestamp: 2016.06.03 07:00:16
Event ID: 35747833
Event Age: 20d 0h 0m

What I am thinking is that the value should be the latest data value or UNKNOWN if there is no value rather than the value at the time just like when you view triggers in the front end

The reason being is that when things are escalated I would think you would like to know what it currently is rather than what it was to allow you to action things depending on these values. If you want to see the previous value you can always go into latest data etc...