Interesting, I'd never thought to look much at other authors output on this topic. There was a post the other day talking about Jules Verne's corpus, and I now wonder what his output was like.
I've another thought on the topic as well, which is that I have a friend who hired a lot of former newspaper journalists circa 08 when there were mass layoffs in that industry. He said they were able to most consistently churn out content for his book over other writers, but that it was significantly lower quality, and needed a lot more rework and polish. For him the tradeoff was worth it, and he organized his time and resources around this increased quantity. But this adds to the idea that you really can't look at pages/day (or LOC/day) on an individual basis either, since it's the whole pipeline that matters. And if you really want to improve total output, you need to look at variables outside of individual contributors. Things like code reviews and QA can perhaps greatly increase total output.