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As the lead author, I can tell you with certainty that several hundred hours of work were involved in updating from MVC 4 to MVC 5. Some of the main areas were in identity / authentication (chapter 7), completely new chapters (e.g. the single page application chapter), attribute routing (completely new for MVC 5), most of the chapter on the NuGet gallery, etc. Even simple things like updating from Visual Studio 2012 to Visual Studio 2013 required reshooting almost every screenshot in the book. The code samples were all updated from MVC 4 to MVC 5 (including all dependent NuGet packages, view updates to Bootstrap based views, etc.).
Also, I spent a lot of time in making the first 5-6 chapters of the book flow more smoothly. Previously, these chapters were written by different authors and we'd heard from lots of readers that it jumped around too much. I significantly rewrote these chapters so they flowed more smoothly.