Greetings -
Whilst I do not have access to the afformentioned book, I was able to peruse a few historical knives thanks to Chuck Burrows who posted an excellent link.
Based on the knives there, and looking at a few of them with butts seemingly larger than the throat by the guard I think I can understand the issue and throw in my 2 bits.
One interesting coffin-handled knife I built from a blank had a two-piece grip frame as I think Chuck described -the blade end had
small tang that the guard was slipped over, then the rest of the larger coffin-shape tang was attached to the blind "mini-tang" .
I am attempting to attach a small pic to further elucidate.
Another option, from my time as a volunteer blacksmith at small hysterical sites, was to initially forge the tang uniformly thick but perhaps an inch wide; then fit the guard; then finish forging the tang into the broader coffin-shape, but with a tapering thickness. The guard can be slid a bit back and forth for final finish of the blade and tang, then driven tight or soldered in place.
The completed knife often confused admirers who posed the question "How the h**l did you get that guard on?"
Whereupon I would wax philosophic regarding the ability of metals to expand on heating and shrink when chilled, and of various secret alloys that were elastic at critical temperatures, watching their faces all the while until someone finally realized their chains were getting yanked....
yhs
Prof Marvel