Dr.EndoIndy said:

It helps to ask what evidence would change your mind before you look at any.

Coming at Dr.EndoIndy’s question from a different direction. Take it one variable at a time. Almost every unanswerable question in these threads is unanswerable because three things changed in the same fortnight, and no amount of subsequent argument can untangle them after the fact.

The figures, for anyone assembling their own picture. If you are comparing against somebody else’s result, check that you are comparing the same measurement taken the same way. Most of the apparent contradictions in these threads dissolve at that step.

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

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

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

jason_paloalto said:

If you are comparing against somebody else’s result, check that you are comparing the same measurement taken the same way.

Pushing back on jason_paloalto here. I think the framing smuggles in the conclusion. Ask it the other way round and the obvious answer reverses, which usually means the question is doing the work.

Closing the loop on my own question.

Closing this out. What actually changed my mind was the point about waiting for a trend instead of reading a single measurement, which is embarrassing in hindsight and worth saying anyway.