See the review of the third edition.
The "preface to the fourth edition" says
Again, we have revised, updated, and significantly extended it for this fourth edition. We have added some classical material that may have been missed so far, in particular on linear programming, the network simplex algorithm, and the max-cut problem. We have also added a number of new exercises and up-to-date references. We hope that these changes serve to make our book an even better basis for teaching and research.
Updated information about the book can be found at http://www.or.uni-bonn.de/~vygen/co.html.