Here’s some information provided by Harley Smith:
The ranges denote the deficiency to toxicity concentrations. The numbers in the () are what he considers the highest that should be provided in a nutrient formulation (not necessarily ideal but wouldn’t want to normally exceed). For instance, sulfur is listed as 400 PPM which is not something you’ll be purposefully formulating.
FWIW, sulfur is something of the wildcard in formulations since plants tend to tolerate excess sulfur. You can balance your macro nutrients in your formulation allowing for excess sulfur containing molecules, such as potassium sulfate instead of potassium nitrate.
Also, what he see as typical ratios for veg vs bloom:
