Greetings from New Mexico, USA!
The book has only been out for less than a year. It likely has decent info in it (I have not read it yet, waiting for a second hand or library copy to come my way) but as some have pointed out there are some possibly major inconsistencies in it that would make one wonder as to the quality of the sources the author relies upon to make his conclusions. I do not believe that this book looks into the origins of Simonov's original trials design(s) and the progression to the SKS-45, it is more an overview of the hardware itself. No one book will appease everyone, but considering the paucity of literature out there we take what we can get.
From what I have seen, this book expands on "The SKS Carbine, 5th Revised and Expanded Edition (For Collectors Only)" by Poyer/Kehaya which had been the primary reference book written about the SKS in the past 20 years. It was last updated in 2020 and still contains some pretty bad errors and omissions that you'd think they would have caught and updated by now. The inclusion of Howie's hand drawn arsenal marking appendix is also a bit of a head scratcher as his list is provably wrong in certain areas (such as including 'arsenal /25\' which we know is a broken /26\ stamp spanning a specific serial # range).
For the SVS-38 I am not aware of anything in book form, and certainly not anything in english. Might be a Russian source out there.
https://www.m9130.info/svt-40 is a very well researched and well presented online source of the Tokarev that Simonov was up against which was finally adopted, and of course there are other pages of varying quality out there among world wide web. There are also pages out there that show other x54R semi automatic and automatic designs that went through trials, but as far as having everything together in a book, I'm not aware of it. Other members may know of some good leads.
Again welcome to the forums, please post away if you have any questions or want to show off any firearms in your collection!