F is the production factory which stands for Fujigen.
The first digit will be the last digit of the year, ie. The last 5 numbers will be the consecutive number denoting production count for the year with the caveat that each month will start at predetermined intervals of 3000 or 5000, etc.
This is where you start seeing consecutive numbered plates on the remaining regular joint models that no longer indicate year.Here is the breakdown courtesy of Ibanez Collectors World.Until 1977 Maxon used 5 digit serials: 1st character is a production code (1,2,3, etc., maybe related to different production location) 2nd character indicates the year of production (2=1972, 3=1973, etc.) 3rd character indicates the month of production (0=January, 1=February, ...A 7 digit number example - C5030567 - translates, 5 = 1995, 03 = 3rd month [March], 0567 = 567th guitar built in March 1995.An 8 digit number example - C03114373 - translates, 03 = 2003, 11 = 11th month [November], 4373 = 4373rd guitar built in November 2003.On typical Ibanez serial numbers the first 2 digits will indicate year, or the first digit will indicate the last digit of the year, but there are also some that indicate no year at all.