When Reed and Malloy are at the Christmas tree lot, a woman runs up and tells them there is a robbery in progress two blocks away. When they arrive, it's raining, although the sun was out at the tree lot. Later, when the sergeant arrives, it's not raining and the street is dry again.
The scene at the parking lot where Officers Reed and Malloy help Mrs. Ward load the gifts into her car is shot from three different angles. In all three, the same black-over-brown 1966 AMC Ambassador hardtop appears in the background - in three different locations.
After Haines cuts Adam-12 off, he passes the same car (the copper Mustang that appeared throughout the series) twice before driving onto a lawn.
(at around 6 mins) The shadows of lights are visible on the hood of the car.
Officers Reed and Malloy are called to settle a disturbance between Charlie and Reba Buehler; this is the second time recently they have done so but they make no reference to having met or dealt with the couple before.