A long time ago I covered a high school basketball game that had playoff implications for the visiting team. The official scorer was a former coach on the home team's football staff and still a faculty member there. I sat near him and kept play-by-play, then after the game checked my stats against his.
The home team won by one point. I kept coming up one point short when I totaled its individual scoring. Then I went back through the play-by-play more carefully. At one point in the game, when I flipped from one page to the next, I copied the score off the scoreboard. Upon further review, the home team was given three points on the scoreboard instead of two (there was no 3-point shot at any time close to this point in the game). I didn't catch it like I would have had it been all on one page, but the flip from one page to the other helped me to miss it. Not sure what I would have done had I noticed at the time, but I brought it to the attention of the official scorer.
He checked his book, and he couldn't make the home team's scoring add up to the total either. He came up one point short. He listened to me, looked at his book, looked around the gym, then said "Oh, I forgot to give so-and-so that free throw. Then he penciled in a point, closed the book and walked away.
Visiting team didn't catch it, didn't protest, didn't make the playoffs.