Roberts mentioned the jacket to a reporter on the afternoon of the murder.
She didn't mention the horn-honking incident until about one week later once the accused assassin himself was gunned down sparking whispers of conspiracy.
So, what's your point?
She couldn't have made a mistake (like Baker and Whaley did) and didn't lie about the zipper on day one, but she did concoct and lie about this police car a week later?
That's some reliable witness, you've got there!
Henry Wade must have busted for joy when Oswald was killed and saved him from having to go to trial with fruitcakes like Roberts as his best witnesses.