The argument that any calibre will do if you hit it in the right spot, relies on the unreasonable assumption that all shots are either "good" or a complete miss.

In truth, there are probably as many shots that are slightly off-centre as any other category.
Taylor's "knock out formula" was based on his observations of this phenomenon. Both that very near misses produced sub-optimal results - such as the elephant getting up and killing you after having appeared to have been dead - and that using a more adequate calibre put the odds more in the hunter's favour.

Bell himself recorded cutting the tail off a "dead" ele to mark his ownership of the animal, only to find, on his return, that it had recovered from its "fatal" head-wound and decamped.

Same goes for many wounds that are fatal-but-not-yet. Whether it is the wound that does not leave an adequate blood trail for tracking in the late evening, or the same slow bleeding that permits the animal to either make cover or make it to the hunter for a little tit-for-tat before expiring.