Paid for independent testing and results did not match vendor COA

A narrower follow-up, since the general answer is now clear:

Why two laboratories report different purity for the same batch, and which number to believe?

Dr.NutriCornell said:

They are not contradictory, they measure different things, and this is the single most common misreading of a certificate.

I do not accept the framing. The question has been narrowed to the version that has a tidy answer, and the part that was dropped is the part the OP actually asked about.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

Dr.NutriCornell said:

They are not contradictory, they measure different things, and this is the single most common misreading of a certificate.

No disagreement, though it depends on where somebody is starting from, and this thread has been assuming a starting point nobody stated.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

Dr.NutriCornell said:

They are not contradictory, they measure different things, and this is the single most common misreading of a certificate.

Bookmarking. The distinction being drawn above is the one nobody else makes. Taking it to my next appointment.

Clinical perspective, offered as context rather than as advice. Whatever the answer turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, and invite the correction. That is slower than asserting, and it is the only version that survives being wrong.