The thread here reminded me of something that happened back in my restaurant days.
I was working at a restaurant as a waiter. The year was sometime between 1986-1989. At this time, I noticed I was getting a slew of $10 bills as payment. All of them were crisp and brand new, and I recall that a couple of people who paid me with two of them had the serial numbers in sequence!
The catch? The year on the bills was 1969!
What happened? Did the treasury open up some old file cabinets and found a bunch of old bills and put them in circulation? Does this happen often? Can we expect to see some shiny new Wheat Pennies any time soon?