I suppose they don't need to know the actual thrust in kN. Just if more or less than currently set is needed. And they get accurate indications about the effects of thrust and thrust changes, in particular vertical speed and air speed and speed trend.
Only analysts such as ourselves might require a physical thrust figure to gauge brake efficiency, etc.
Maybe IAE has some kind of graph to convert EPR to thrust in KN having barometric pressure (altitude/air density) and air inflow speed (aircraft speed) as aditional parameters.