Has an NFL game ever ended 12-9?
It has. 12-9 has been a NFL final 19 times in 18,234 games. The first was Chicago Bears beat Chicago Cardinals on October 15, 1933; the latest was Indianapolis Colts beat Denver Broncos on October 6, 2022.
That makes 12-9 the 267th most common final score out of 1,095 that have ever occurred in NFL. One point away, 13-9 has happened 35 times and 12-10 has happened 21 times. At one point the score disappeared for 43 years, between 1933 and 1976.