Has an NBA game ever ended 99-81?
Yes. NBA has seen a final score of 99-81 34 times. It first happened on March 2, 1988, when Denver Nuggets beat Cleveland Cavaliers, and most recently on December 9, 2015, when Charlotte Hornets beat Miami Heat.
That makes 99-81 the 700th most common final score out of 3,189 that have ever occurred in NBA. One point away, 100-81 has happened 21 times and 99-82 has happened 33 times. Nearly all of its occurrences fall between 1980 and 2009.