Serial numbers on F cameras are in blocks. The first block was 64, with numbers starting at 6400001, running through 6499999. Subsequent blocks were 65, 66, 67, 68, 69, 70, 71, 72, 73, and 74. The 66 block was never finished. Not even close. A little over 2000 66s were produced, then the numbers were changed to 67. Also, the 74 block was not filled, as the camera was discontinued at serial number 7451052. Later numbers may be found, however, as Nikon supplied replacement top plates with serial numbers already engraved into the 746xxxx range.
It should be noted that the myth about the first two digits of the serial number indicating year of manufacture. It is partially true, and only by coincidence. The first cameras were sold in 1959, with a serial number block of 64xxxxx. At some point the serial number prefix did coincide with the year of manufacture. Production ended in 1974, in the 74 serial number block.
The first hundred or so cameras are different than the later batches in several ways. They were probably more of a pre-production run. The wide levers were solid, except for a hollow tip. The pins on the prism finder that the body locks on to are triangular.
Still among the first few thousand, the self timer lever changes from a cross hatch pattern on the early ones, to a set of vertically running ridges. The original finder was engraved under the front "Nippon Kogaku Japan". It became painted on, then changed again to "Nikon F Japan". The wind lever changed from completely hollow to solid.
The photomic meter prism was introduced in April, 1962. It would not fit on older cameras without cutting away part of the back of the prism well on the body. Cameras coming from the factory already modified were marked with a red dot engraved next to the serial number. I believe that all cameras where so marked once they started, although research shows red dot and non-red dot cameras intermixed in the 658xxxx and 659xxxx serial number range. I suspect this was due to camera not being assembled in strict serial number order rather than being produced both ways concurrently. To me, it just wouldn't make sense to continue making cameras that would not accept the new finder as they are neither more expensive or more difficult to make. But that is just my theory.
The small batch of roughly 2200 66s are also marked. When they skipped to the 67 block, the dot was dropped. If you have a camera in the 64 range, or 65 without the dot, the meter finder could not be mounted without modification. The modification was fairly simple, and would be covered up by any finder that was mounted. Quite a few have been so modified.
In September of 1966, the Nippon Kogaku logo was replaced by the word "Nikon". This was part of a trend in which the logo, and eventually the name Nippon Kogaku would be replaced by the name Nikon.
The next change would be to the nameplate on the front of the camera. With the release of the final meter prism for the F, the FTn, a slightly different front plate was needed for the new method of locking the finder. It is a very subtle difference in appearance, but noticeable if you try and mount an FTn finder on too early a camera.
The final change came about during serial number block 73. The F2 had been released, and the F was given a cosmetic facelift to make it appear to be more consistent in styling with the F2. It aquired a new plastic tip to the wind and self timer levers. This version is identified as "F with F2 cosmetics, or (for some unknown reason) Apollo F.
There were other small changes. At some point the bezel surrounding the finder release button was given a slot. This allowed easier use of a fingernail to release the finder and screen without extra danger of accidental release. There are differences in the ASA scales on the bottom of the back, and the color of the plastic insulation on the flash synch.