Here's an article with similar data that does into the source of the data. http://www.techdirt.com/articles/20120330/12402418305/why-missing-20th-century-books

Here's an article with similar data that does into the source of the data. http://www.techdirt.com/articles/20120330/12402418305/why-missing-20th-century-books-is-even-worse-than-it-seems.shtml http://www.techdirt.com/articles/20120330/12402418305/why-mi... It was posted here a few months ago.