Inputs and effects are inconsistent in game files?

For example, in policies.csv we see that AdultEducationSubsidies has an effect on Education, but AdultEducationSubsidies is not listed as an input to Education in simulation.csv - what does this mean in terms of the calculations?

What difference is there between defining an input in Y from X, or just adding an output in X to Y?

GDP and CO2Emissions are another example - GDP has CO2Emissions under its effects, but CO2Emissions does not have GDP as an input?