Back to the Future
The license plate OUTATIME was too perfect to pass up, but it wouldn't actually work in reality if you want to be exactly like Doc Brown. The state of California has a max cap of 6 characters on the license plate. OUTATIME as one extra letter, therefore making it an illegitimate plate!
Forrest Gump
Forrest Gump fell victim to a small oversight by the prop designers. The letter that Forrest got from Apple applauding him on his investment is actually super inaccurate. Apple wasn't a publicly traded company until 1981. The letter is obvioiusly dated in 1975. Maybe they wanted to use a big name and didn't care about the details?