Paid for independent testing and results did not match vendor COA — looking for input

Adding the clinical framing, because it changes how the question reads. Order of operations matters more than any single choice here: establish a baseline, change one thing, wait long enough for it to express itself, then measure again under the same conditions.

That is the short version; the long version is somebody else's post.

SleepDoc_PDX said:

Shipping damage protocol for vendor vetting orders: if your package arrives with visible damage, temperature excursion, or broken vials: Photograph…

Coming at SleepDoc_PDX’s question from a different direction. They are not contradictory, they measure different things, and this is the single most common misreading of a certificate. Purity is a relative area measurement: the main peak as a percentage of total peak area in the chromatogram. Content is an absolute mass measurement against a reference standard. A vial can be 99% pure and contain 6.1mg — pure material, overfilled — or 99% pure and contain 3mg, which is pure material and a short fill. Purity tells you what fraction of what is there is the right molecule; content tells you how much of it there is. You need both, and a certificate with only purity is telling you half the story.

One concrete data point for the thread. One habit that pays for itself: post the method alongside the number. A figure without its method cannot be checked, and an unchecked figure is how this community accumulates folklore.

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?

Moderator note: two posts asking for a source have been merged into one. Please search the thread before asking again.