A few curious details about this lens:
The dot in "NIKKOR-P.C" is always low like a full stop. On almost all other Nikon rangefinder lenses (and later in F-mount lenses) the dot is mid height, eg "NIKKOR-P·C". Early NIKKOR-S.C 8.5cm 1:1.5 lenses also have the low dot, but somewhere around no.264xxx the dot changes to mid-height. There are three batches of the NIKKOR-P.C 10.5cm 1:2.5 with the low dot, roughly between 817312 - 818144, another batch from 819834 - 819908, and the last batch from 912501 - 912800 (based on information collected so far). All the rest of production have the mid-height dot. The NIKKOR-P.C 8.5cm 1:2 is the only lens where all lenses use the low dot.
Somewhere in the mid-1950s, Nikon dropped the "·C" designation, because coated lenses by then had become standard. The 8.5cm 1:2 was the only lens to carry the ".C" mark right to the end, even though it continued to be made through to the late 1950s and early 1960s.
At the same time the "·C" designation was dropped (or a little after on some lenses), Nikon changed the font for the engraving on the lens. For example, the old font has a "3" with a flat top, the newer font has a rounded top. The newer font continues to be used for F-mount lenses right up to AI-S lenses still made today. However the 8.5cm 1:2 lens uses the old font even for the latest black series that Ric reviewed, except for a few very late lenses such at the one shown here:
http://kevincameras.com/gallery/v/nikon_rf/lens/85_2/black/497666/ (the latest serial number I have seen). Even this one has the front ring engraved with the old style, but new font on the focus and aperture scales!
Many late production lenses with black barrel and modern styling are often engraved "J. PAT. 188,481" near the base, but it is often missing, with no clear pattern that I can see.
It seems that whoever engraved the parts for this lens was somewhat removed from the rest, they continued to use old styles even after the rest had changed. A unique lens