When Perry and Della stop to allow Brander Harris out of the car, Della turns around in her seat. While doing so, her coat extends onto the dashboard, where it is obvious that the front windshield is not there.
When Perry pulls up in front of the police station to drop off Brander Harris, it is obvious stock footage in the background.
When Paul is outside the phone booth copying down the number that Leora Matthews is calling, his view is blocked by another man. He reports to Perry that he got DA (that would be the Dakota exchange), and then 670 blank blank. Paul would have seen her dial 3 then 2 but why would he convert that to DA, which he can be seen writing down, rather than record and report the actual numbers dialed.
Paul Drake buys a newspaper in the hotel lobby and sits down to read it. But when he holds it up, it is plainly a single sheet of large paper with a banner headline on one side and a blank page on the other.