L1 and L6 have mounting ears as part of the case casting because they mount in a slider behind the cover panel in the dash, the ears enable it to be retained with 2 screws.
L8 is mounted in a tray behind the glovebox and clips into the tray, so doesn't need the retaining lugs.

Bear in mind though that it is possible to swap the internals betwen casings to enable them to be mounted either way, so just looking at the outside doesnt neccesarily tell the whole story.