to quote my copy of the vintage guitar mag price guide “f-serires dreadnought flat top 1969-1981. The Fseries were Japanese-made flat-top acoustics, included were concert- and dreadnought-size instruments with features runnubg from plain to bound necks and head stocks and fanmcy inlays, there was also a line of f-series classicals, nylon- string guitars. Alable on the inside indicates the model. FC-20 is a classical with Brazilian rosewood. There was also an Asian (probably Korean) import standard series for 82-90 where the modles start with F.
1969-1981 Higher- End solid top 125-250
1969-1981 Lower-end Laminated 100-150
1972-1981 FC-20 Classical 150-275”
Hope this will help you.