If you try to upload a book from the Internet Archive that is already on Commons you will get the error message: A file named '[IA indentifier]' already exists on Wikimedia Commons. However, a number of IA books have already been uploaded in low quality PDF format and IA Uploads in djvu format would be vastly superior to these PDF versions. I understand that we do not want masses of duplicates on Commons, but if IA Upload could allow duplicate uploads in both file formats, users could improve the quality of Commons uploads significantly.