Other mistake: When the show aired in 1990, in the pilot episode Brenda falls for Jason. She later on reveals herself to be a "16 year old junior" in high school. Season 2 opens up with the gang on summer break which technically would make them going into their senior year. It wasn't until Season 3 that they were going into their senior year. They graduated in 1993 from West Beverly but the show debuted in 1990 so technically they should have been sophomores.
Beverly Hills, 90210 (1990)
Episode list - season 1
More mistakes in Beverly Hills, 90210
Brandon Walsh: It was good to see you back at the Peach Pit tonight. I know it took a lot of courage.
Brenda Walsh: Brandon, please, I've had quite enough praise for a while.
Brandon Walsh: All right, you're a huge loser. How's that?
Brenda Walsh: Oh, much better.
Trivia: When Brandon and Kelly leave the movie theater, they pass a billboard for The House of Yes, which co-starred Tori Spelling.
Question: Was Valerie Malone introduced this season to balance out Brenda's departure?
Chosen answer: Yes, she was.