Found mistakes at 5.21 and 5.22.d

Thank you, for the input, this will be corrected in the next update.

1-3 times per year, depending on changes. I think one is not far off. We cannot change things one at a time in real time as the entire course has to be swapped out, so we batch changes. That's one reason forums are useful to watch for errata

Thanks for your careful analysis