Revealing mistake: When Jerry is in the tunnel and Morgan blows up the drone, Jerry hides behind the front of a car. Then he runs to the back, but he is shown again at the front of the car.
Revealing mistake: When the Porsche Cayenne is lifted out of the water at the scrap yard then placed on the ground, if you look through the gap between the front passenger wheel you can see the engine is removed from it.
Revealing mistake: When Jerry jumps out of the building to escape the FBI, when he lands it does not look like Shia LaBeouf but a double.
Answer: I think it was to show that Jerry and Rachel maintained a friendship after it all. Also to maybe, maybe hint about some kind of romantic future in the way that Rachel says, "you remembered", when her ex-husband was said to never have remembered Sam's birthday.That's my thoughts - I think it's just to let us know how the characters turned out.