Seriously, it is very possible that Hurrell was guessing as the book was being written, based on his experience, about what he probably-sorta-kinda-possibly-maybe used for that special shot of "X", on that special day years earlier.
I don't know if there were notes taken by Hurrell or not, but I do know that I don't keep any camera setting records and only very crude notes penned on the boxes of my materials on hand.
The practical question is probably not "is the book is a true historical record?" though, but instead "is the information contained a reasonable guide?"
The latter seems likely and given the current market availability of Super X, at best the book gives you a reference of the type of film he may have chosen, liked, or got paid to say he used. Given that uncertainty, it would seem the specific answer is purely academic in nature.
Also given the maliability of most any film's/paper's characteristics/responses though development and exposure and filters on the lighting and Filters on the camera and ... It gets to the point where what Hurrell actually used no longer matters.
Most masters, in any trade or craft, get to a point where they can make various tools do the same work.