In regards to the book you've mentioned, I have no knowledge or experience with that particular book, so I can't directly endorse or condemn it. However, from looking at what they provide in the "Search inside this book" link located just below the image of the book cover, and then looking at what is put forth as the book's "Table of Contents" it sure doesn't seem to cover everything, as far as what's listed it only mentions the "Main Rod." Also on that "Table of Contents" page there is listed "Part 1, Main and Side Rods" and "Number 79."
So in my mind the following questions arise; 1) Does the "Part 1, Main and Side Rods" indicate that Table of Contents listed only reflect a partial listing of a chapter with in the book, or what? or 2) Does the "Number 79" represent that this is the 79th book in a series of books that in total cover all areas of building a steam locomotive?
As to what you referred to as a "generic" water injector. In my experience of looking at various documents depicting various areas of steam locomotives. What I've found is, the only thing that is generic is the concept of what the job of an injector is. What each manufacturer's version physically looks like, just where it's located, and how the pipe connections from the tender to the boiler were laid out. Those particulars are all over map, so to speak. Unless you are speaking of one particular locomotive in a given time frame.