End of game questions

Play #1: Team A had the ball in their frontcourt with 5 seconds left. B1 slaps the ball out of A1's hand, and the ball hits out of bounds on the endline. L blows his whistle and puts his hand up to stop the clock. Just after he blows his whistle (.5 seconds by my guess), the horn sounds for the end of overtime. We convene and agree that the whistle came before the horn, but none of us had definite knowledge of how much time was remaining. Under NFHS rules, can we add time? What knowledge do we need to put time back on the clock?

Fyi, I already read the case plays and rules concerning timing mistakes and ending the period plays, and couldn't find anything.

Play #2: Team A has an endline throw-in with 1 second left in the period. A1 throws the ball to A2, who catches and immediately shoots a three-pointer. Time expires as the ball is in midair, and the horn goes off. I am C, opposite table, and I have last-shot responsibility. I signal to count the basket. The three-point try occurred in T's area tableside. As I am signalling to count the basket, T is making the made three-point signal. Couple questions. Should I signal to count the basket and then signal a made three to mirror the T? Or do I just signal to count the basket? If I signal that the three-point try did not get off in time, but is made, should the T immediately drop his made three-point signal?

Another question about this situation. Endline inbound for team A. 1 second left, A2 catches the ball, takes a dribble, then releases the three-point try. However, the timer starts the clock late. This gives A2 the time to dribble, shoot, and release the ball before the horn sounds. Can the officials do anything to disallow the shot which clearly would have been late if not for the timer starting the clock late?