So many things can make a difference. Method of grow, state of growth, root conditions, temperature, humidity, strain, CO2 levels, different formulations, TDS of water and of course lighting and cycle lengths. Want to really be surprised check out high pressure aero or atomizer grows. Top TDs about 500 to 600. Using only intermitient spraying so total water used is about 10 to 20 percent of that with standard hydro or low pressure aero. Spray warmer water say mid 80's and use goes up as does growth speeds but still much lower water use than standard hydroponics etc.
All the s things that can make things different and still people follow manafacturers labels based upon some unknown average needs. Go figure. What is a normal average with that many variables having effects.