not sure on the testing, I literally do not test in reefkeeping except for salinity and temp as nothing else is required *when* you have a system that permits large water changes. when you have to conserve water changes due to mass gallonage, individual param control is important. if I had large tanks id own a few.
that is the range among our nonscientific kits.
test tube graduation marks vary, dosing procedures vary, titration habits vary it all adds up to the ranges you see and then actual test kit physics could be at fault, who knows. api ammonia certainly has physical challenges.
your question highlights something that I think is shocking though. what if your highest end kit turns out to be right, but lets say you had a bit less nutrient so that it read 8 ppm accurately....what would that red sea read then, 0?
so that means ten thousand people who either own those lot [HASHTAG]#kits[/HASHTAG], or are running the method w similar variables, might read zero nitrates and indeed there could be 8 ppm, see how profound that hidden detail is?
causes cycling hysteria. why did my cycle stop? threads.
cycles do not ever stop

and to test nitrate and nitrite isn't harmful, but its not required either for cycling (for nutrient control detailing its fine) and to test them in cycling adds two more steps unneeded, and two more misreads to make you doubt the cycle process. only ammonia is required.
nitrate is always being made when ammonia goes from some to zero within 24 hours in a biosystem, whether we see that nitrate or not on a test doesn't matter, our testers aren't awesome they barely get us by, yet we base them as foolproof and make thousand dollar decisions off them. I will now link your thread to that cycling thread for showing us the nitrate ranges of two common and massively popular kits
only ammonia from a reliable kit needs to be traced out to cycle a tank, neat info. a way to carve off the insanity into something universally repeatable.