In the opening dance sequence Julie's shoes change from heels to flats as she's dancing near the fountain.
DJs Raechel Donahue and "Rodney on the ROQ" Bingenheimer from radio station 106.7 FM KROQ are hosting the high school prom. Rodney didn't make event appearances after the 1970s.
After the fight at the prom, Randy and Julie run out and get into a Chrysler limousine and drive off, only to be seen minutes later sitting in a Lincoln Town Car limousine stopped at a red light .
"Promposals" are a contemporary tradition. It's highly unlikely that a boy in the early 1980s would've asked his steady girlfriend to prom in such an elaborate way. He likely would have assumed she was going with him.
When Randy goes to the skating rink's restroom, some urinals have automatic flush sensors. These just started being used in the early 1990s.
Th skateboards used in the movie are twin-tails, which didn't exist in the 1980s.
Julie and her friends are preparing for prom at the time of the Sally Ride's first space shuttle mission, which occurred on 18 June 1983. Prom season in Southern California in the 1980s was April and May and school was out for summer after the second week of June.
Julie comes home from shopping at the mall while her dad is watching the 18 June 1983 launch of the space shuttle Challenger in broad daylight. Challenger lifted off for that mission at 4:33 a.m. PDT and shopping malls in Southern California opened at 10:00 a.m. in the 1980s.