An incredible source covering more than a century of operations, predating the revolution, and spanning all continents. The first book dives quite deeply into this exact topics, with double, triple and sometimes quadruple crossings. I loved the part about the prep for large-scale sabotage in eastern seaboard of USA in the events of hostilities, something I had no idea about but would have been quite an bold move. There was also a lot of unbelievably dumb stuff.
The book mentions the increased difficulty of doing anything undercover or assumed identity in the modern digitally connected world. All of those undercover things are pretty much the thing of the past now, with OSINT being able to find just about anything about anyone.