Books can be attributed to "Unknown" when the author or editor (as applicable) is not known and cannot be discovered. If at all possible, list at least one actual author or editor for a book instead of using "Unknown".
Books whose authorship is purposefully withheld should be attributed instead to Anonymous.
I finished up skipping fairly big sections as the material lost relevance for me. I worked in the field of testing for years; some of Boris’s initial statements I disagreed with but then came round to as I could see his point of view. The book has a lot of depth and masses of cross referencing of some deep academic materials, BUT I’m not sure I could rocked up at the place quoting it as a bible.