They changed a box in the wall of a garden apartment I used to deliver to. Behind it was a letter with a 22 cent stamp as postage. It had to have been from before 87/88 because that’s when stamps went up to 25 cents.
We also found an express mail when getting a bad out if the hamper that was apparently never checked to make sure it was empty, the express was from three years before we found it. Going from Chicago to Chicago. It somehow ended up in New Jersey.