PharmacoVig_BOS said:

Keep the original post as written when you update it, and add the correction underneath.

That reframing is the part I needed.

Reporting back.

Update, and it is the boring outcome: nothing was wrong. The measurement I was reading had moved less than its own week-to-week variation, which somebody said upthread and I did not believe.

mark_tokyo said:

Update, and it is the boring outcome: nothing was wrong.

This is my experience too, for whatever a second data point is worth. The detail I would add is minor and it is already implied above.

mark_tokyo said:

Update, and it is the boring outcome: nothing was wrong.

There is a second half to this that has not been said yet. Whatever the answer turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, and invite the correction. That is slower than asserting, and it is the only version that survives being wrong.

Happy to go further on any of that.

Adding the numbers, since they settle part of this. Say what you would expect to see if you were wrong, before you look. It is a small discipline and it changes what you notice.