I haven't reread the book in many years, but my memory was that the ban wasn't actually on killing but rather on 'shedding blood.' It's still impossible to believe, but I think that the figleaf for the regime was the idea that death that didn't spill blood didn't count.

But at the end of the book, bloodshed that hadn't yet become (and possibly might not be) lethal counted. If that counted, shouldn't a fist fight that resulted in a bloody nose also count?

The book worked really spectacularly well when I was eight and had no concept of how very, very long a thousand years was.