On the page with copyright, ISBN, and so forth of a book fished out of a Little Free Library, the following paragraph appears at the top:
If you purchase this book without a cover you should be aware that this book may have been stolen property and reported as "unsold and destroyed" to the publisher. In this case neither the author nor the publisher has received any payment for this "stripped book."
Indeed. Bookstores always were able to return unsold stock to publishers for credit. In the case of paperbacks, they could strip the front covers of unsold copies, and send those back, saving themselves on shipping costs, and the publisher on storage. Going on fifty years ago, I worked for a department store that set out the "stripped books" in an area open only to staff. As I recall, I read Play It As It Lays and all or most of The Peter Principle in stripped paperbacks. Whether it was the chain's policy to offer the copies to staff or it was just the decision of the store management, I can't say. I suppose that every copy the staff took was one that the store didn't have to pay to dispose of.
That was about it for my stripped book reading. A few steps from me there is a copy of Beyond the Hundredth Meridian missing its front cover, but that cover was loosened by reading. I don't know whether in the age of Amazon retailers still strip covers. For one thing, computerized analysis has given the big wholesalers much better control of their inventory. For another, a publisher might require some daring to demand the covers of its unsold paperbacks back from Amazon.
The notice was not on the first page one would see were the cover gone. In fact, it is on a verso page, where it will be noticed only by chance, or because some went went in search of publication data.