Firstly, it should be known that a detail can have a source marker and linked markers, or no markers at all. A source marker is the original marker, the first one that was created for that detail. A linked marker is when the source marker is either copied (drag a copy) or when the source marker has been linked to a different marker, via the detail settings dialog. A detail with no marker is an independent detail, and they can be created by deleting the source marker, leaving just the detail window and it's contents (if any), or by creating an independent detail from scratch.
Secondly, it helps to understand the detail icons:
The ones at the top of your list show details that have their source markers on the floor plan. [Project-Based Floor Plan Detail]
The next ones show details that have their source markers in a section/elevation. [Project-Based Section/Elevation Detail]
The next one shows a detail whose source marker has been copied, and the original deleted. [Independent Detail with Marker]
The last ones show details that have no markers at all. [Independent Detail]
In the first two cases, you can find the source marker by right clicking on the detail in your Navigator/Organizer and selecting 'Select Detail marker on the Source view and zoom to it'.
In the third case, there is no source marker, just linked marker(s), so you can right click on it in your Navigator/Organizer and select 'Find Linked Markers...', which will bring up a dialog listing all the linked markers.
The fourth case has no markers, so there's nothing to find.
Hope that helps.
Cheers,
Link.