When Jim pulls the cord to knock the dresser over onto Duffy, one can see the end of the cord is attached NOT to the dresser, but to the door frame, revealing that the dresser was actually knocked over by means other than the cord (someone on the set).
On the close up of Stu's driver's license, even though it states he was born in 1933, the place reserved for his age is blank.
When the marked police car pulls up in front of Rockford's trailer, both the front and rear doors are open. If you look closely, you can see the door jambs are painted a very light shade of blue. It is likely that this car - apparently a Dodge - was purchased used by the studio and given a quick black and white paint job (which looks great).