memoir: edit pass on beginning of pt. 3

This may have been suboptimal task ordering (it would be weird if I
ended up getting tired and shoving something out the door in 2023
where the beginning was tightly optimized from me having started an
edit pass "from the top" so many times, but the middle was a rough
mess), but that's not important; sustained engagement with the ms. is
our limiting resource and is approximately always a good thing.