How much can you do in 0.7 seconds???

[Berkut]

Team A is down by a point or two.

There is 0.7 left on the clock.

A1 inbounds to A2, who is in the backcourt with his back to the basket.

A2 receives the pass, turns, dribbles, then heaves up a 3/4s court shot.

Ball leaves his hand before the buzzer sounds, basket is made, A wins.

Now - the question here is - can an official dis-allow the basket on *any* basis? It isn't a case where there is a "by rule" cannot get a shot off, obviously. In this case, I don't know if it was legit - supposedly people have said that

A. There was 0.0 on the clock, but the horn had not sounded, and
B. The timer did not start the clock the moment A2 got the ball.

I don't know if either of those things are true though.

However, lets assume for the sake of argument that both of those things ARE true.

1. Should whoever is making this call be going by the clock, or the horn? What if the clock is not really readily visible? What if it is readily visible - does that change the answer to the question?
2. If you have reason to think the timer did not properly start the clock, but do NOT have definite knowledge, can you do anything? What if it is even more clear - say there is 0.5 seconds, and A2 actually takes even more time, but the clock operator does not start the clock?
3. Once the call is made - is there any recourse? Lets say the covering official signals a good basket based on not hearing the horn before the ball was gone, but afterward realizes (maybe with the help of his partners) that there was no way the player could have gotten the shot off, or realizes that while the horn had not gone off, there was 0.0 on the clock. In other words, depending on the answers to 1&2 above, can the official change his call after it is made if he is given additional information?

High school rules of course.