Why two labs can report different numbers on the same sample

The lot number check is the whole of what an individual can verify. Everything else is somebody else's document about somebody else's vial.

To the opening post rather than to the thread: Dara, this is my version of it.

Something I got wrong early was treating a high figure as the end of the question. It is one measurement of one sample on one day.

Dara, I have been where you are and I would rather say so than stay quiet.

What I found is that two labs with different gradients can resolve a close-eluting impurity differently and give two honest, different answers.

The mass check and the purity check answer different questions and I did not understand that for a year.

What helped was reading a certificate line by line with somebody who knew what each line was, which took twenty minutes and changed everything.

The suppliers with hundreds of independent results have a record you can look at as a series, and a series is a much stronger thing than a snapshot.

Something worth knowing: a representative certificate and a lot-specific certificate are different documents and only one of them is about your vial.

The reconstitution question is separate from the analysis question and people conflate them constantly, including me for about six months.

What surprised me was how willing the well-documented suppliers were to send the lot-specific document the moment I asked.

What Tor described happened to me too, in a slightly different order.

Something I have learned is that the impurity profile is often more informative than the headline number, and it is rarely discussed.