kate.chem said:

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

I am going to disagree with the direction of travel here. The thread has converged on the tidiest answer rather than the best-supported one, and those are not the same thing.

kate.chem said:

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

True, and it depends on a baseline nobody has stated. Without knowing where someone started, the same number can be an excellent result or a disappointing one.

kate.chem said:

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

Thank you for spelling out the reasoning rather than just the conclusion. Sending this to two other people who asked me the same thing last week.

Adding the clinical framing, because it changes how the question reads. 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.

LibrarianMeg said:

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…

Adding a me-too, because a thread of one person's experience is not much use. Nothing to add that would improve it.