9.3 producing the minimum required specs are legal....rather simple.......
Which is why the 9.3x64 is a great caliber, although sadly eclipsed in popularity by the .375 H&H. It might have turned differently had the Germans won the two World Wars, but I am digressing. Actually darn few makers still chamber for it and load ammo for it, which is really too bad, because it is arguably every bit as good as the .375 H&H, and people in the know would argue that it is actually better, because more efficient with its ahead-of-its-time fat beltless magnum design, short enough to fit in standard K98 action. A great round indeed

(Note: I guess the newish 9.3x66 Sako, with performance roughly halfway between 9.3x62 and 9.3x64, also qualifies, but who has ever seen one in Africa?)
Which is also why the 9.3x74 R in double rifles is about impossible to get to legal standard because messing up with high pressure loads invariably wrecks havoc with the regulation, not to mention the risks of overpressure in break open rifles

(Note: forget the 9.3x72 R...)
And finally, as previously mentioned, which is why the 9.3x62 is problematic because getting the 9.3x62 to legal standard can only be achieved by loading over SAAMI pressure (ooops!), or lighter bullets at higher speed, which is not exactly a smart move, as Robertson indicates

Not to mention that it is difficult to demonstrate the legality of the load in the field when arguing with a local government official well decided to show the whities who is boss...

(I know that it is unlikely ...
until a problems arises, in which case you will be crucified if you have even one toe over the legal line.)
Anyway, there is no convincing some in the 9.3 fan club 
that 9.3x74 R, sadly, is in fact illegal in many countries for Class A game, and the 9.3x62 is, hmmm, let us just say problematic, and I am not trying to do so
I am just providing factual answers to legitimate questions. Some may like it, some for sure dislike it, but facts are facts, and unless I am confused the question was "9.3x74 R on Buffalo", and the answer stands, in Robertson's own words:
-- "not strictly legal",
-- "adequate for buffalo - even if only marginally so",
-- "little is gained by speeding up these two calibers",
-- "lack frontal surface area and consequently stopping punch",
-- "relatively light recoiling".
That's all there is to it, and it is what it is, and everyone will make their own choices, but, hopefully (
and is not it one of the main purposes of Africhunting.com?) with full knowledge of the facts
So.......... yes "9.3 producing the minimum required specs are legal" but it is NOT "rather simple" 
because 9.3x64 is all but a unicorn nowadays; 9.3x62 or 9.3x74 R effective DG commercial loads (286 gr bullets) do NOT produce the minimum required specs; and getting loads to do so either exceed SAAMI specs (never a good idea!) or drop bullet weight to increase velocity (never a good idea either in DG loads).
PS:
On a personal note, I actually like the 9.3x62 (and ballistic twin 9.3x74R), because "even if only marginally so", it IS "adequate for buffalo", and as previously mentioned, it is the round I selected for my petite wife's DG caliber, because her limitations fit Robertson's description. I certainly wish the regulations would change to lift this legal limbo that always makes me uncomfortable, but it would be irresponsible to hide it from newcomers or encourage them to break the law...