A certificate of analysis documents a specific batch at a specific point in time. The question buyers rarely ask — and sellers rarely volunteer an answer to — is how often a new COA is actually generated as new batches come in, versus how often an old one just gets reused across many later shipments.
What Should Trigger a New Test
Industry good practice (as followed by sellers who take testing seriously) calls for a new COA per manufacturing batch or lot, not per product listing — meaning the same listed product should carry a different COA every time the underlying batch changes, even if the price and packaging look identical.
“If the batch number on the COA doesn’t match the batch number on your vial, you don’t actually have a COA for what you’re holding.”
— a quality-assurance consultant who reviews testing documentation for several sellersHow to Tell the Difference
The giveaway is whether the COA’s lot or batch number on the document matches the lot number printed on the vial in hand. If a seller can’t produce a COA whose batch number matches what’s physically in front of you, the document isn’t verifying what you’re actually holding.
Why This Gets Skipped
Retesting costs money and time per batch, and a seller under pricing pressure has a direct incentive to stretch one COA across as many batches as buyers will accept without checking.