What does “99% purity” on a peptide COA actually tell you?

Something I think gets overlooked when reading peptide COAs is that purity, identity and content aren't the same thing.

A reported 99% HPLC purity result relates to chromatographic purity under that analysis. It doesn't automatically establish identity, the amount of material present, or that every possible contaminant was tested.

When reviewing a COA, I think the better questions are:

• What analytical method was used? • What does that method actually measure? • Who performed the analysis? • Can the report be verified? • Does it correspond to the actual batch?

There's a more detailed illustrated breakdown here for anyone interested: peptidegrade.uk/research/how-to-read-certificate-of-analysis/

Curious what everyone else checks first when reviewing analytical documentation.