For this particular product, it doesn't matter what the publication year of the book is. 1) The quotes are short and 2) the use of them is transformative, so this falls squarely within the doctrine of Fair Use.

That said, I'm sure if an author or publisher of a book that's still within copyright contacted Author Clock and asked them to remove their quotes from the database they probably would, because it just wouldn't be a thing worth fighting about.