EXFO OTDR 2 - Manual (Page 206)

Description of Event Types
198 OTDR
Merged Event
Not All Event Types Are Tested
In this situation, the only thing that we can clearly know is when the loss
has a Pass status. If the global event loss is less than or equal to the
smallest threshold value (a value that is tested, of course), we are sure that
the merged event status is Pass. Otherwise, we cannot know, so the status
of the event is Unknown.
In our example, if we suppose that you chose not to test non-reflective
losses, then the analysis would be done as shown below:
Pass
Unknown
0
0.5
1.2
Pass
Unknown