When the villains catch up to the Pink Cadillac at the car wash, a gunshot is fired into the windshield. Later, the windshield is perfectly intact.
In several different scenes vehicles are shown being parked and left in the alleys between the casinos in Reno, Nevada. Due the chances for robbery as well blocking the egress and exit of emergency vehicles, this has not been allowed in many decades. In fact, one of the fastest ways to get your vehicle towed in the city would be to park in an alley and leave it.
When the Pink Cadillac is first uncovered, Bernadette Peters extends her rear end and passes wind; which can be clearly heard on screen.
When Nowak is held at gunpoint in Jeff and Dinah's place, he throws the keys to Roy's Cadillac to Roy. After the ensuing gunfight, Roy leaves with Waycross in a different car, presumably taking the keys to the Cadillac with him, as he does not want anybody to drive his car. Yet, the next morning Nowak and Lou Ann drive off in the Cadillac without issue.
(at around 31 mins) A boom mic's reflection can be seen in the car's window.