Analytical methodology, documentation, handling, and storage — written for people who have to make a reagent work, not for people shopping for claims.
A certificate that reports one purity number is telling you a fraction of the story. Here is what each section establishes, and what a missing section usually means.
Purity is one axis of quality and the easiest to optimise for. Four other failure modes will ruin an experiment just as thoroughly, and none of them appear on a purity line.
Temperature is the variable everyone controls. Moisture, oxidation and light do more damage to a sealed vial, and get less attention.