Is it fair to say: as the higher the COD value, as polluted the discharge waters are? Say the positive or negative statement.

Yes higher the COD value higher it is polluted, as COD value indicates amount of organic matter present in wastewater

Yes , if the river have COD value under the limit

and

No, if the river have COD value over from the COD effluent and over the limit

yes my friend you can say that, when we talk about COD its the amount of oxygén needed to degrad organic matter chemicly, so every molécule of water consumed in this optic is going to be removed from the the natural environment of unloading. all this gonna cause asphyxiation middle, eutrophication

The higher the COD means the higher the inorganic matter and the higher the BOD the higher the ornganic pollutant load. So for domestic sewage the BOD is 200 mg/l  COD the will be around 400 mg/l, but when treated they will be much lower and so less of a pollutant to the environment.

Yes, the higher the COD the more polluted the waters are because this just simply means more oxidizable material, organic and inorganic are present in your water which are pollutants.