In this case, not that many lens samples to collect. Roland Vink says only around 1000 units ever were made.
It may be much less than that. In the pre-Ai series, official figures suggest 29 units with serial numbers 628001 - 628029. I have records of 7 lenses from 628003 - 628024 so that seems about right.
The AI series starts where the pre-AI series finishes, starting at 628030. I have seen only 4 lenses with serial numbers 628035, 628042 which match well with the start number. The next number jumps to 628147 from a Nikon brochure (number not very clear). Then a big jump to 628556 sent to me by a collector.
The AIS series has a new serial number block starting at 629001. The earliest I have seen is 629004 on ebay in 2011. Then a big jump to 629400, 629410, 629415, 629417 and 629435. Of these three were sent by message with no picture so I can't be 100% sure there were no typing mistakes.
If serial numbers for the AI and AIS versions are continuous, I would expect to have seen many more by now. Maybe the missing lenses were bought by government/military/industry and never survived? Or they were never made in the first place with big gaps in the series, in which case production may be as low as 100.
What's the serial number of the the one at the NG event? if anyone knows of any other lenses which could help to fill out my data, that would be great.
I have seen one 6mm 1:2.8 in person. It was no 628007 on display at the Nikon store in Paris back in 2004. At the time I was corresponding with a French Nikon user/collector called Bruno Najac who showed me and my then Fiance around Paris. We had a great time, but we sadly lost touch with him(still married to my now wife!)