Well, I think the contention was that during high tension, they might not take the time to be sure. As for the Indian Ocean (Reagan era) explosion, I never heard that the analysis was changed from an asteroid to a nuke test. Where'd you read that?
I did a quick Web search and found out about the 1979 Vela detection of an explosion that has been labeled a South African nuke test by a lot of people. But though I remember reading about it, I can't find any Web pages about an explosion over the Indian Ocean that caused the DoD to think about waking up President Reagan in the middle of the night. But I know it happened. Oh well.
Saw a reference recently to a possible SA/Israeli joint program. SA later stopped research and production when they realized that they could not retain administration of their program during the inevitable regieme change.