ADDENDUM to the review of _Mark Twain's America: A Celebration in Words and Images_. By Harry L. Katz and the Library of Congress. Little, Brown and Company, 2014. 244 pages. Hardback. $40.00. ISBN 978-0-316-20939-7._ by Harry L. Katz and the Library of Congress. By Kevin Mac Donnell Since the appearance of my review of this book on November 5, 2014 on the Mark Twain Forum, several developments make it appropriate to bring members of the Forum up to date. At the time my review appeared, I calculated that only about 125 of the book's 244 pages (excluding the preface, foreword, acknowledgments, picture credits, bibliography, index, illustrations, and extended quotes) were actual _original_ text. Now that I've taken some careful measurements, the number of pages of original text stands at about 98. Quotes (mostly from Mark Twain works) constitute about 30 percent of the book's main text alone. When I wrote my review, my list of errors and significant omissions stood at 75, but by the time I responded on November 17 to Wiener and Katz's letter to the Forum, that number had grown to just over 100, thanks to the help of other readers. It now stands at 118 and is still growing. Some of the book's erroneous statements (such as the remark that Henry Clemens was older than Sam) are contradicted in other passages, giving the book as a whole the appearance of having been written by a committee that never met to compare notes. Its readers should not be told such nonsense as the grandchild Mark Twain never saw was born three days before he died, that Susan B. Anthony was a candidate for U.S. president, or that the United States annexed Hawaii in 1848. My original review mentioned that _Mark Twain's America_ copied passages from two unacknowledged sources--a fact that Katz and Wiener have now publicly admitted. I can now report that their book copies from at least three more unacknowledged sources. Moreover, borrowings from one of these sources may rival or even exceed the more than 400 lines taken from Rasmussen's _Mark Twain A to Z_. The author and editor of _Mark Twain's America_ said the two unacknowledged sources I identified in my review were "mistakenly omitted" but they did not say anything about the other sources now known. They also said they "seek to be as accurate as possible in [their] work" and would "rectify errors or omissions in forthcoming editions of the book." If they are sincere in those sentiments, why not rectify part of the problem immediately by posting a complete list of their sources? The e-book and future editions should be halted until these issues can be addressed. It was anticipated that a complete corrigenda would be posted in this Forum. That must now wait. Identifying and correcting errors is the responsibility of authors, not reviewers, just as it is the responsibility of the authors to reveal their sources. Now is the time to do both. It is the right thing to do.