They shoot proofreaders, don't they?

Whoever read my library's copy of The Masque of the Black Tulip has added all these corrections in the margins. It's not just spelling and typography; some of them call out the author for anachronistic dialogue or historical inaccuracies. Did they really not have lump sugar in Napoleonic times? This is why I always disliked buying used books in college; sometimes you couldn't tell if the previous owner was stupid or not.