[3-4] After I NREVERSE a list, it's only one element long. After I SORT a list, it's missing things. What happened?

These are particular cases of the previous question.  Many NREVERSE and
SORT implementations operate by rechaining all the CDR links in the list's
backbone, rather than by replacing the CARs.  In the case of NREVERSE, this
means that the cons cell that was originally first in the list becomes the
last one.  As in the last question, the solution is to store the result
back into the original location.