750,000 F3's make sense, at the height of the 35mm film era. I have 5 of those. 240,000 F4s makes sense as well, I have 4 of those. What's the F5 numbers like? Probably more than the F4. Lots of pros I know and myself still have and shoot that. Out of the at least 65 pro's I know in my area (PJ's, editorial and wedding shooters) the only one who had one F6 was trying to sell it to me. One. How many do you Know of being used? Yours and your friend and ...?
From my understanding about the F6 is that the shutter unit and body casting was designed alongside the D2/D3 era cameras, making it quite easy for nikon to keep producing F6's in small amounts. As in 50 per month...
Even if the production was over 200 per month for the first few years 34,000 still seems very high. A top tier high performance 35mm still camera produced in the digital era at high prices to a dwindling market. Hey I'm glad they still make them, love to get me a couple, but serial numbers aside, not many are out there. Just aren't. I'd be stoked if there were that many around, it increases the chances I can find one! Best regards