Has an NBA game ever ended 99-78?
Yes. NBA has seen a final score of 99-78 19 times. It first happened on January 13, 1951, when Rochester Royals beat Ft. Wayne Zollner Pistons, and most recently on December 31, 2014, when Los Angeles Clippers beat New York Knicks.
That makes 99-78 the 1001st most common final score out of 3,189 that have ever occurred in NBA. One point away, 100-78 has happened 9 times and 99-79 has happened 26 times. At one point the score disappeared for 37 years, between 1950 and 1987.