1999 Catalogue of Errors on U.S. Postage Stamps by Stephen R. Datz (1998, Paperback)

You will find any book written by Stephen Datz to be an important and enjoyable addition to your philatelic library. I have well thumbed 1986, 1996/97, and 2000 editions of his Errors Catalogue in my stamp room. Any edition of this Catalogue will provide a wealth of information to help you identify, value, and understand the production processes that create Errors, Freaks, and Oddities on United States stamps.
Datz's 1999 Catalogue of Errors is well organized and full of data about Imperforate and Color Omitted Errors such as the printer, date of issue, production process, and current value. Datz also provides an estimate of the quantities known for each error (something you will not find in a Scott Catalogue). The introduction and final chapter alone are worth the cost of the book because they provide a comprehensive overview of imperfs, color errors, misperfs, foldovers, miscuts, color shifts, gutter pairs and gutter snips, open creases, inking errors, ablinos, and other EFOs.
I only give 4 stars to the 1999 Catalogue of Errors because it does not cross-reference Datz's numbering system to Scott Catalogue numbers. The Scott numbering system is Copyright by Amos Philatelics, Inc. dba Scott Publishing Co. Datz's 2000 Catalogue of Errors is published by Krause Publications, which publishes the rival Krause - Minkus Standard Catalogue of U.S. Stamps. Apparently Datz could not get Scott's permission to use their numbering system when he switched publishers. (The 1996/97 edition was published by Sanabria.)