Trustme:
The date was punched into the die, individually at the time.
The central devices were on one central die (punch) and then the date was added.
If it was sunk too weakly, the die dinker would simply 're-punch' the date into the die.
That is why there are varying positions for the dates on old coins.
Today, of course, all parts of the coin, including the MM, are sunk into the die at one time (single press). No more doubled dies, theoretically, at least.