When Jim pushes Angel onto the chair in his apartment, there's a box of Sugar Frosted Flakes and a vase that appear and disappear depending on the camera angle.
The mail collection boxes shown are blue with red tops, but the red tops were changed to blue making the boxes all blue in 1971.
At the house of James Rockfield, where the package was delivered, Rockford learned that it had arrived "Special Delivery." But Eddie purchased stamps, hand addressed the package, and dropped it in an outgoing mailbox at the train station. In those days Special Delivery required either a special pickup or a trip to the post office. (Note: The package had been sent to Rockfield's house by the "Nixie Clerk" at the Post Office).
When Angie and Coke leave Rockford's trailer, the parking lot background is obviously a matte painting.