I’ve spent the past 30 years as a freelance copy editor for nonfiction books and other documents, and have worked for dozens of publishers. The short answer to the question of errors that make it into the published book is that publishers don’t want to pay for quality.

Many tasks in the life of a manuscript are now handled by freelancers, and in some cases every step except project management is outsourced. So that’s one issue, that managers might not have access to the best copy editor out there. But another issue is that good copy editors—like me!—get tired of doing what amounts to pro bono work: when publishers pay very low project/page rates, they’ll get lower-quality work. When I accept work from publishers who pay a low rate, I read it only once then skim once more quickly. It’s far from ideal, and leaves lots of bugs no doubt, but it’s what they’re willing to pay for.

On the other hand, I have other clients who pay by the hour, and tell me to spend as much time as needed to catch every error. With those clients I read three or sometimes four times, and very few errors slip by me.