Yes, that's so! I also did not believe and ordered twice.
It fits only the combination Nikon FM2 / FE2 Okularschutzglas with Nikon Dk-3 Eyecup. This combination is of the eye cover equal to the DK 19th
The adapter with eyecup I do not always use. For videography or photography with Live View is much the eyecup in the way, especially created. So it pays to carry the original shell.
Otherwise I can only recommend the adaptation. Light shield 5 Stars.