This lens is not listed in any brochure or manual. I think it was introduced just shortly before the whole NC series was discontinued.
The lens is very compact and the focusing ring is quite narrow. This might also be the reason that the focusing action is not quite as smooth as with the other CS lenses. On one of my two 50 mm 1:2 lenses I own, the focusing even got completely stuck at one point. I had to take the lens apart and clean the helicoid.
The optical performance is also excellent and almost equals that of the 1:1.7 version. Another advantage is its very low weight.