For a 16-bit adc, the smallest difference it can detect is 1/2^16 = 0.0015% of Vref. For a Vref of 5v, that's about 75uv.
You will find that in an industrial environment, it is incredibly difficult to keep all kinds of disturbances to your circuit to be materially less than 75uv - typical smps has ripples of 10 - 100mv for example. You will also find that to make your software consistent from one build to another, your divider will have to be at least that accurate or you have to compensate for it in software.
What you are trying to achieve is very difficult from an engineering point of view.