Should I create an SDS from a single substance or build a mixture?

It depends on what you're documenting. If your product is one pure chemical — like our AC-99 Acetone SDS — Section 3 just has a single ingredient row 1. If it's a blend, like PC-150 (a propan-2-ol / propan-2-one solvent), you add it as a Mixture and Section 3 expands to show each component with its own percentage and hazard codes 2. Either way, ExactSDS rolls the ingredients up into the same Physical / Health / Environmental hazard summary automatically.