(Art. 2a) Penalized if discovered before ball becomes live to start game.

Is this penalized?

Scorer makes discovery as R approaches circle.
R tosses ball.
Ball tapped by A1 to A2.
Horn, Whistle by U.
Scorer notifies R of the error.

T or does this not count as discovery before ball is live?

Either book? Why would they be using more than one?

Very tricky question, because while you say that the scorer discovers the error prior to the ball becoming live, it isn't recognized by the officials until after the ball has become live.

You also don't say what the error is that was discovered by the scorer. If the error is that one of the players in the game was not a designated starter, then it is too late to penalize this because the ball has become live. Any other item covered in the list could still be penalized at this time.

Copying Error
 

In case there is an error in copying. I'm not going to penalize the visiting team if the home scorekeeper incorrectly copies the numbers. If there is a #30 in the visiting book, and #20 is copied by mistake into the home "official" book, I'm not penalizing the visiting team if #30 is in the game, and the scorekeeper brings it to my attention that, "There is no #30 in the book".