1) In 1989, Iraq and the US were allies and there was no reason for the US to worry about Iraq invading Kuwait hence the 1990 misunderstanding which resulted in Iraq thinking the US ambassador had tacitly approved the invasion plan.
2) if the UK and US wanted to stop the ANC getting hold of the nukes and had the cooperation of the apartheid regime, it could have just decommissioned the lot in exchange for cash or a relaxation of sanctions.
3) if the UK wanted to stop the ANC getting nukes, it would have bought all of them, not just a couple.
4) what is the point of a nuclear power secretly acquiring a nuclear bomb? If it were ever used everyone would know.