No cartridge, rifle or handgun, will give a 100% guaranteed one shot stop. Physics doesn't allow it.
While I do believe this to be true, I have my doubts about the 90mm recoilless rifle..(with a COM hit, of course)..
.327 Federal Magnum, for example, listed energy figures on the ammunition when it was released, because the American Eagle 100 gr soft point load met the 500 ft-lb energy requirement for hunting big game in certain states; and the other loads included the information to show that they came up shy (and were illegal in those states).
until you mentioned it, I had forgotten how now, many states include an energy requirement in defining what is legal for what game.
In light of that, putting that number on the ammo box makes good sense, providing a handy "in the field" reference that shows your ammo meets the requirement. (or doesn't).