By that description it looks like I have 3- NOT AS OLD, 1- NEWEST. of the EL-Nikkors. This is just something that I was curious about since I had a few and they are all different in how they are physically different from each other. I guess they were made one way until the molds wore out and then changed the style and shape. ( Just thinking )
I have one 75mm that stops down to f45 and the others are 50mm that stops down to f16.
They used the same "EL NIKKOR" name for both the four-element and six-element lenses. The 75mm is a four-element lens. The 50mm f2.8 is six-element and the 50mm f4 is four-element.