I think this may have something to do with entries that were replaced by another entry.. The test entry I have does have a value in replacedEntryId member of the baseEntry object. I was able to determine this by "undeleting" the asset, then setting display_in_search to 2. This made the entry returnable by baseEntry->List.
Perhaps setting status=3 and display_in_search=-1 is how Kaltura hides replaced entries?