Other mistake: After the pool massacre, when the shooting stops, at the left of the screen and right off the policeman's helmet, a man sits down and then lifts the beach chair up.
Other mistake: When Callahan meets Sunny in his apartment lobby and she asks him, "What does a girl have to do to go to bed with you?" Callahan replies, "Try knocking on the door." and if you look behind Callahan at the Trolley going down hill, you can see a kid waving to the camera.
Other mistake: When Harry and Early Smith are in Lt. Briggs' office, Briggs' first name on the desk nameplate is spelled "Neil", but when Harry and Early Smith leave the office, Briggs' first name on his office door is spelled "Neill."
Other mistake: The vigilante bike-cop slaps a supressor on his Colt Python. A suppressor on a revolver doesn't work without serious modification. There's only one revolver I know of which would be able to use a suppressor, namely the Russian Nagant M1895. And that's due to the gas-seal system in the cylinder, which seals all the out-gassing, only letting the gases out the muzzle-opening. (01:01:00 - 01:10:00)
Other mistake: In the final credits, DiGiorgio is misspelled as "DiGorgio."
Other mistake: In the end credits, Callahan is misspelled as "Calahan". (01:56:50)
Other mistake: Before the shooting, we saw a reflection of the officer in the outside mirror of the limo. The glass is rectangular. The actual mirror of the '73 Cadillac Model 75 had rounded corners.
Other mistake: When Ricca is pushing his way through the crowd, just after a man yells "Ricca, you're a killer" a shot of the crowd shows a sign saying "UP YOUR RICCA" which makes no sense. Surely this sign was meant to say "UP YOURS RICCA." (00:03:50)
Other mistake: In the scene where the mob boss gets interviewed in the garden atrium after being freed, the news media pushes up to get really close to the podium. Note that the first reporter, dressed like Gilligan, trips and almost falls into the podium. He catches himself but has to keep his head down during the rest of the shot.
Chosen answer: The error didn't necessarily start with the makers of the credits. It could have crept into the process at any point. Whoever typed up the names to give them to the technicians who made the credits could have misspelled the name.