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

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

lisa_labSD said:

Say what you would expect to see if you were wrong, before you look.

Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. I would resist the confidence. Half of what this board was certain about two years ago has since been quietly dropped, and nobody went back to correct the threads.

I would rather be corrected than agreed with, if it comes to it.

lisa_labSD said:

Say what you would expect to see if you were wrong, before you look.

Agreeing with lisa_labSD, and the qualification matters more than the agreement. Yes, and the corollary is less popular: if the reasoning holds, it also holds where it produces an answer we do not like.

lisa_labSD said:

Say what you would expect to see if you were wrong, before you look.

This answered a question I did not know how to ask.

Reporting back.

Reporting back for the archive rather than for the thread: I did the narrow version of what was suggested, gave it the full interval, and it settled. Posting it because threads without a follow-up are half a thread.