Around 1971-1972, Nikkor lenses began transitioning from being labled "Nippon Kogaku Japan" (often abbreviated NPK in listings) to being marked Nikon. Most lens designs from the period are easy to find marked either way. I personally prefer the look of the Nippon Kogaku markings because they fill the indentity ring nicely, where as the Nikon-marked lenses often have blank space:
Besides the obvious branding reasons for the change, it is understable that reducing the amount of engraving on the identity rings would save time and money. Note they also droped the "No." before the serial number. The order of the information also changed slightly:
Nippon Kogaku Japan No. XXXXXX Nikkor-Q Auto 1:3.5 f=135mm
Nikon Nikkor-Q Auto 1:3.5 f=135mm XXXXXX
In the later "K" era they dropped the "Auto" markings as well as the letters indicating the number of elements in the design, further reducing the amount of engraving. I assume this is also why they eventually switched from "Lens Made in Japan" to just "Made in Japan".
However for some designs Nippon Kogaku-marked copies are rare, and you are more likely to find Nikon-marked copies. I am excluding lenses that were only available marked Nippon Kogaku or only available marked Nikon as well as exotic lenses for the time being. As usual all this information and much more is available on Roland Vink's incredible Photosynthesis site.
28mm f/2 N:
Only about 3000 were marked Nippon Kogaku, about 11000 were marked Nikon and another 15000 were marked Nikon with the "·C", although all these versions were multicoated.
35mm f/1.4 N:
Only about 3000 were marked Nippon Kogaku, about 9000 were marked Nikon, and another 7000 were marked Nikon with the "·C", although all these versions were multicoated.
105mm f/2.5 P (newer black front design):
Only about 1000 were marked Nippon Kogaku, some 64000 are marked Nikon. These are so rare KEH doesn't seem to know they exist, they seem to think all Nippon Kogaku-marked 105mm lenses are the older design with the silver front ring.
180mm f/2.8 P:
Only about 1400 were marked Nippon Kogaku, about 15000 were marked Nikon. Only about 3000 were multicoated "Nikon P·C".
500mm f/8 reflex
Only about 3600 were marked Nippon Kogaku, about 13000 were marked Nikon. These don't seem to be particularly hard to find despite their rarity.
80-200mm f/4.5
Only about 2200 were marked Nippon Kogaku, about 23000 were marked Nikon. These seem to be undervalued: I don't think people realize they are so rare.
Conversely, there are all some lenses where the Nikon marked versions are rarer than the Nippon Kogaku lenses. The most notable example is the 45mm f/2.8 GN though.
45mm f/2.8 GN:
About 24000 were marked Nippon Kogaku, but only around 7000 were marked Nikon. The multicoated "Nikon GN·C" verison is also uncommon with about 13000 made.
200mm f/5.6 Medical:
About 6700 were marked Nippon Kogaku, only around 1500 were marked Nikon. The multicoated "Nikon Medical·C" is the most common with some 10000 made.
50-300mm:
About 8500 were marked Nippon Kogaku, only about 5700 were marked Nikon. The later K, AI, AI*ED, and AI-S*ED versions are all rare as well.
1000mm f/11 Reflex:
All the versions are rare, but there were about 1200 marked Nippon Kogaku, about 900 marked Nikon, and the multicoated "Nikon Reflex·C" version is also rare with about 1500 made.
Most of the focus unit lenses are more common marked Nippon Kogaku or multicoated than marked Nikon, although all the versions are rare.
400mm f/4.5 Q:
About 1300 marked Nippon Kogaku, 600 marked Nikon, 400 multicoated.
600mm f/5.6 P:
About 1200 marked Nippon Kogaku, 750 marked Nikon, 1000 multicoated.
800mm f/8 P:
About 450 marked Nippon Kogaku, 350 marked Nikon, 620 multicoated.
1200mm f/11 P:
About 240 marked Nippon Kogaku, 150 marked Nikon, 380 multicoated.
