A certificate is only worth something if you can read it. Five checks, in this order, and you know whether the report belongs to your vial and what it says.
Step 1: the batch number
Start with the number on your vial’s label and find it at the top of the certificate. If they don’t match, you can skip the rest: the report is about different material. If there is no batch number at all, the certificate by definition can’t be linked to what you have in hand.
Step 2: the chromatogram
Look for the graph of the HPLC analysis. You want to see one clear main peak and a flat baseline around it. A percentage without a graph is a claim; with a graph you can see for yourself whether it holds. Watch the scale of the y-axis: a heavily zoomed-in view makes small side peaks look bigger than they are, and a zoomed-out view hides them.
Step 3: the retention time
The retention time is the moment the main peak leaves the column. That value is characteristic of the peptide under the conditions used. Compare it with earlier batches of the same product: a clear shift means something is different about the material or the method.
Step 4: the mass
Mass spectrometry confirms the identity. The measured mass should be listed next to the theoretical mass. The two may differ by a fraction at most; if the difference is larger, the sequence is wrong or there is a modification.
Step 5: the residual values
At the bottom are the measurements that have nothing to do with purity but everything to do with usability: moisture content, endotoxins and residual solvents. A high moisture content means you have less peptide in the vial than the weight suggests, and that the material degrades faster.
Missing one of these five? Ask for it. A supplier that has every batch analyzed simply has the data on file.