One lot is one lot: when a report becomes a pattern — the long version

I disagree with the reply above, and I think the disagreement is substantive rather than terminological.

The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.

Temporal patterns: if results from a supplier were good two years ago but have deteriorated recently, that is information. If they have been consistent over years, that is also information.

Pattern across lots: a single result is a data point. Three or four results from the same supplier showing a consistent pattern becomes a record worth discussing. Two results that disagree might just be measurement variation.

On post #14 — agreed on the reasoning, with one qualification.

Dosing and purity: a vial that is 99% pure might contain 80% of its label claim if the other mass is water, counter-ion, and excipient. Purity and content are different. Both matter for different reasons.

This follows post #16 rather than contradicting it.

Blind submission is worth the effort: have someone else relabel the sample so neither you nor the laboratory knows which supplier it came from until the result is back. Blind results change minds; self-selected results do not.

Structured report format: compound, lot, independent testing service, method as reported, result, and the certificate figure for the same lot. One lot is one lot. It becomes a pattern at three or four, and it becomes a disputed record when asked and not explained.

Lot matching: confirm the lot number on the certificate matches the lot number on the vial. A result from a different lot is not evidence about your vial.

Testing service selection: Janoshik gives purity with chromatogram. Medutest gives combined purity and identity. PeptideMeter gives verification records as well as results. VendorInvestigate reviews documentation. They answer different questions.

Worth separating two things that post #19 runs together.

Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.

post #23 is right about the mechanism and I think understates the practical bit.

Multiple services on one lot: agreement across two independent laboratories is stronger than a high number from one. Our vendor pages deliberately mix services for that reason.

Coming back to post #23, because the follow-up matters more than the original answer.

What "verified" means on our pages: specific lots were independently measured on stated dates by named services and results were consistent with the supplier's documentation. It is not a recommendation and does not extend to untested lots.

Disputed records: when a result disagreed and was not explained, the record says disputed and stays that way. We do not remove inconvenient history; we document it.

Date the report: when the analysis was done matters. Material can degrade in storage. A report from two years ago is still useful but is not evidence about the current state of the same supplier's stock.

post #27 answers the question as asked. The question underneath it is different.

Date the report: when the analysis was done matters. Material can degrade in storage. A report from two years ago is still useful but is not evidence about the current state of the same supplier's stock.

I read post #27 twice before replying, because I had assumed the opposite.

What "verified" means on our pages: specific lots were independently measured on stated dates by named services and results were consistent with the supplier's documentation. It is not a recommendation and does not extend to untested lots.

This follows post #27 rather than contradicting it.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.