In addition to what Robin mentioned below, some of these placeholders are for books on our Wanted list. I also think it's useful to show readers that particular

In addition to what Robin mentioned below, some of these placeholders are for books on our Wanted list. I also think it's useful to show readers that particular books are looking for volunteers to produce, and also to show that some books they might want are locked away by copyright for possibly decades. In that sense it's partly a political message.