Some countries have used undated coins or coins with a "frozen" date (for example, they keep producing coins for 10 years, but they all have "1905" on them). One problem: if they reconfigure their coinage, it's easier to say "everything from 2005 and earlier must be redeemed or it becomes valueless." Without a date, it's harder to communicate that info.

Of course, not putting dates on coins would save trillions of dollars and may be the cure to all these economic crises.