Sprites and similar phenomena have been reported for many years by pilots and others, but scientists didn't believe them until recently because it didn't fit their flawed models. It's similar how scientists didn't believe centuries of stories about rogue waves from mariners until one was recorded with a buoy in 1995.
Pecos Hank, the best storm chaser on Youtube, has recorded beautiful video of sprites: https://www.youtube.com/watch?v=tGPQ5kzJ9Tg