"Same batch" isn't proof

Suppliers often say an order is "all one batch." That matters, because one good test would then speak for the whole order. But the claim is only as good as the evidence behind it.

The claim vs. the evidence

"These 500 vials are one lot" is a statement. It becomes evidence when vials are picked at random from that lot, sent to an independent lab, and the report is tied to that lot number. Without those three steps, a single old COA can end up standing in for material it never tested.

Why random, and why every lot

• Random, so the sample can't be picked out as the good ones.
• Every lot, because a pass on an earlier order says nothing about the next one. A lot that tested well last time and a lot that arrived this week are different material.
• Independent, so the lab has no reason to want a pass.

What a sample can and can't tell you

Testing a few vials from a lot can't prove every single vial is identical. What it does is catch a lot that isn't what it was claimed to be, which is exactly the failure that matters. The honest phrasing is "every lot is sampled and tested," not "every vial is tested."

What to ask

Ask a supplier: how many vials per lot do you test, how are they chosen, which lab tests them, and what happens to a lot that fails? A supplier with a real process can answer all four. The full list is on the supplier checklist.