Dr.AddMedPHL said:

The honest answer is that the effect is real, the magnitude is contested, and the individual variation is larger than either.

This was answered several pages up and is worth repeating rather than re-litigating:

Pushing back on the consensus forming here. Consistency is not the same as correctness, and a board that agrees with itself quickly is usually agreeing with the first person who sounded certain.

Worth restating a point from upthread for anyone joining at this page:

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.

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

Closing the loop on my own question.

For the archive: it took about six weeks rather than the two I expected, and the difference between those two numbers was the whole of my problem.

VendorMark said:

For the archive: it took about six weeks rather than the two I expected, and the difference between those two numbers was the whole of my problem.

Careful with the causal language. Two things moving together in a period when five things changed is not a mechanism, and stating it as one makes the thread less useful to somebody reading it later.

VendorMark said:

For the archive: it took about six weeks rather than the two I expected, and the difference between those two numbers was the whole of my problem.

No disagreement, though the timescale matters more than the mechanism here. Most of what looks like a difference in kind turns out to be a difference in how long somebody waited.