The Nikkormat FS is a Nikkormat FT without built-in light metering system and mirror lock-up feature. Even if proposed at the time at a lower price than the FT, the FS did not meet great commercial success and according to the serial numbers found on the Web (from 7400xxx to 741xxxx), the number of units produced has most probably been less than 20,000.
This explains its relative rarity compared to other Nikkormat / Nikomat.

There is no known copy of the FS in black finish.

Like the FT, the FS has undergone some design changes during its production years. Among the known evolutions there is the frame counter whose window is initially a clear plastic convex lens pasted on the top cover (as above on the photo, between the film advance lever and the shutter release button) then which is improved by the addition of a metallic ring. This change occurred somewhere in serial numbers [7406940; 7407310] range.
On the "Camera Chronicle" Nikon web site, Nikon justifies this change by indicating that this window "looked cheap and was prone to scratches".

The Nikkormat FS does not seem to have been imported into France as can be confirmed by its absence in the French distributors catalogs (and available on the site at the time of writing) for the period 1965 to 1973.

If all sources agree to date the production start of the Nikkormat FS in 1965, it is more difficult to give a production end date. According to sources, this goes from 1967 (Nikkormat FT production end date) to 1971 or even 1973.

The existence of a Nikon brochure "Nikkormat, The camera for very selective photographers" dedicated to the Nikkormat FTN but mentioning the FS as an alternative to FTN suggests that the FS was offered some time after the FT stop date. In this brochure, the Nikkormat FS is mentioned in these terms: "If you're the fastidious type and prefer to conduct your own exposure judgement, Nikon also offers the Nikkormat FS, which is identical with the FTN except that it does not have the independent mirror lock-up control and the built-in metering system. But, of course, it accepts the same inter-changeable Nikkor lenses and Nikon F accessories."