Can a vendor reuse one COA for every batch they sell?

No. A certificate of analysis is tied to one specific batch or lot. It only describes the material that was actually tested, so once a new batch is made the old COA says nothing about it. That's why the batch number is the thing to check. The lot number on your vial should match the lot number on the COA. If they don't match, the certificate isn't describing what's in your hand. A generic or recycled batch reference showing up across many shipments is a known red flag. Third-party labs make this checkable. Janoshik's portal (verify.janoshik.com) lets anyone enter a batch reference and pull the original test data, then confirm the purity, identity, compound and test date match the COA. A batch that was never tested won't verify. Research use only, not medical advice.