Finally I've found an early All black Nikkor 50mm f/1.4.
As you can read in the books by Bob Rotoloni, these are rather special light weight lenses. These "early black" lenses weigh one third less than the normally produced lenses. The first series is from 1953, so before the appearance of the black Nikon S2, and in about 400 pieces. At that time the Nikon S was produced. The black Nikon S is extremely rare, only a few were made, so why the early all black Nikkor 50mm f/1.4 was made? Only because of the lower weight?
It is possible that Nikon had plans for a small series of Nikon S cameras in black, but that these plans were cancelled because the S2 was well underway. It can be that at that moment the order to produce the All black Nikkor was already given. The Nikon S was a heavy camera, so maybe Nikon decided to make the lens for the black Nikon S as light as possible.