Those pdf are useless since they are not measuring the health of the fish in any sort of scientific way. They simply state the condition of their water as measured. A study would have a control condition in which at the end of the some period the fishes organs, tissue, general health and similar between a control and experimental group was compared.How do you explain the information in the attached documents then?
Also I'm not sure i understood their condition - 150mg of nitrate seems pretty high. They are also claiming the discus are perfectly happy in fairly hard-water - i can't actually comment here if tank raised discus adapt to hardwater or the longevity (or overall health) of a discus in hard water vs soft water; i do know there are quite a few species of fishes that don't do very well in hardwater with regards to longevity but i can't say with authority if that does or does not applies to discus.
Having said that i suppose if a fish longevity is 15 years in perfect condition and only 14 years in harsh condition with no other ill effect at the end of the day it probably doesn't matter much but ....