I might have been more inclined to stick with the anywhere outside South Africa rule, but exclude Lesotho and Swaziland from that rule for obvious reasons. Or maybe go as far as excluding Namibia, Botswana, Zimbabwe and Mozambique as being international, simply because it is quite possible and easy, to drive into one of these and place a cache/TB.
Just my 2c worth.
My take / vote would be that local only includes "common border" countries - Lesotho, Swaziland, Zimbabwe Namibia, Mozambique, Botswana.
Any others are international. So Zambia, Tanzania and Angola would be international, together with Madagascar, Mauritius etc.
Another 2c
PT