According to Nikon's official "1001 Night" and Roland's serial number list, Noct Nikkor was discontinued in 1997 or 98. So, there shouldn't be any "2006-" version.
The "second version" Michael is referring to should be the later, 9-blade Ais version as opposed to the earlier, 7-blade one.
I used the later Noct, Ais 9-blade version on Kodachrome 25. It was an amazing lens. It was not only sharper than 50/1.2 wide open, but its color rendition was noticeably different from that of "usual" Nikkors, thanks to its excellent contrast and acuity. The 8-milimeter of difference of focal length was larger than you would imagine. The shallowness of DOF would be well comparable to that of Leica Noctilux 50/1.0.
What I didn't like about Noct was that its huge barrel-shape distortion when used at closer range, maybe 1-2m and closer. Also, I didn't like the cut-out of the bokeh circle caused by the symbiosis of its huge rear element and mirror box. The cut-out would disappear in close ranges where the rear element gets further away from the opening of the mirror box, but not in the portrait range. I thought that a rangefinder camera without the mirror box (in the film era) was more suitable body for such a fast Gaussian design lens. In this digital era, a mirrorless body should be more suitable for the same reason.
According to "1001 Night", Nikon used specialized equipments to test the optical performance of Noct Nikkor. I also felt that its mechanical parts like the focusing helicoid and the aperture ring were made under tighter tolerance and their operations was well comparative to that of Leica M lenses. In short, it was of a different class in every respect.