That’s a voltage divider, so the value doesn’t matter much. The original MS20 uses 100k, the Schmitz clone a 47k, and 4.7k might just be a typo in Clacktronics’ layout that Sam based his design on.
Also potentiometers aren’t very precise things, even quality ones are usually ±20％ so designing a circuit where the 6% difference between 4.7k and 5.0k mattered would be madness 
(and 4.7 multiples aren’t really a thing these days, pots use the 1/2/5 series)