u/ZealousidealEagle195

I got these books from a little free library, and noticed this banner at the top of 2 books. (photo included). It says ‘Uncorrected proof- not for sale’. I have an idea about what it means but I wanted to know if anybody has any thoughts on what that is for, or can give me some information.

Hope I posted this in the right subreddit, please tell me if there’s a better one to post this in, Thanks!