JennaRN said:

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

I read this differently from JennaRN, 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.

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.

TrialNerd_Beth said:

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

Adding the part of the answer the thread has not reached. The useful move here is to separate what is established from what is widely repeated. Those two sets overlap less than the confident tone of most write-ups suggests, and the second set is where nearly all the disagreement on this board comes from.

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

One thing that is still open after julia.endo’s answer:

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

OP back with an update, since a thread like this is useless without one.

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.