Other mistake: At the start when Crewe's girlfriend says "don't you take my Maserati" Crewe says he has earned it. He then goes out and gets in a Citroen, not a Maserati. Also, a Citroen front license plate appears on the car shortly afterwards which wasn't there before. (00:03:57)
Suggested correction: The Citroen SM model has a Maserati engine.
That doesn't make it a Maserati. Citroën bought Maserati in 1968, but their badge determined the brand, not what engine was in it. A lot of car companies are owned by other car companies to have multiple divisions in their lineup. If someone has a Toyota and called it a Lexus, they'd be wrong, just like it's wrong in this case.
Other mistake: While reading a book in the Hall of Records, Jake notices some names are pasted in. One of the pasted in names is spelled "Clarence Speer." The name comes up again as Jake Gittes and Evelyn Mulwray are driving away from the orchards. The name is spelled in the subtitles "Clarence Speer" and Jake pronounces it "Clarence Speer." Later Jake and Evelyn are reviewing the Mar Vista Rest Home Activities Board. Here the name is spelled "Clarence Speers." (01:07:35 - 01:17:25)
Other mistake: In the original version of the film there's a mistake in the opening credits where Colin Blakely's name is misspelled as Colin Blankey.