Dr.NateNeph said:

International shipping tracking for cross-border ordering orders: my experience with customs in the US when ordering from overseas: Held at customs…

I read this differently from Dr.NateNeph, on substance rather than tone. Import rules are jurisdiction-specific and this board keeps giving US-shaped answers to non-US questions. What is a personal-import allowance in one country is a controlled-import offence in another.

Ask again with the specifics and you will get a better answer than this one.

The figures, for anyone assembling their own picture. The boring version of this is the one that works, and the boring version is: measure a baseline, change one variable, wait, measure again under the same conditions. Nobody wants that answer and it is still the answer.

Correct me if the detail matters more than I have assumed.

TrialTracker_MD said:

Import rules are jurisdiction-specific and this board keeps giving US-shaped answers to non-US questions.

There is a second half to this that has not been said yet. 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.

One thing that is still open after sarah_TO’s answer:

How would you tell the difference between that and the alternative explanation?

Reporting back.

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.