I wouldn't be surprised if most of the experiences described in the book are those of two men; one of whom was in the Rollbahn and the other in the "Grossdeutschland".
The book begins more or less ordinary until the friends volunteer for the "Grossdeutchland" after which the story becomes extraordinary and I don't think extraordinary is the correct word for those experiences.
I wouldn't be surprised to learn that the author experienced and wrote about life in the Rollbahn but he ghostwrote the experiences of another man who volunteered for a combat unit but couldn't talk freely about it, particularly in postwar France.
In the book we're told the combat unit was the Grossdeutchland but the volunteering and misplaced cufftitle locations open the possibility in my mind that the man volunteered for a combat unit whose cufftitles were worn on their left sleeves.
Excellent points; what you wrote is what I was what my gut told me but I hadn’t been able to articulate it. I think you are pretty much spot on.