Yes, this is kind of a pointless post since it doesn't answer the question in the title. Instead, they just show that the "default" number of digits is enough.
JPL needs the number of digits in a double float because JPL needs to use double floats because JPL is performing engineering.
Paradoxically, double floats are engineered to provide more digits than you need because you need more digits than you need when engineering because if you don’t have insignificant digits to drop, you don’t have enough digits.
