Do all coins have dates?

Modern coins generally have dates, telling which year they were released.  Or, at least a year close to release.  Many coins are, like automobiles, released a few months early.  And in one rare case the Perth Mint released three years o lunar coins when finishing p series one, some years in advance.  Occasionally, a problem exists and coins are not ready for release during the year stamped.  I doubt the would be melted down by the mint.  But, the date approximates the release.

The real problem comes with ancient coins  Many were released prior to a calendar being in place, so they cannot have a date stamped on them.  some of these can be dated by evens they depict, like a military victory, and by who is on the coin.  

Some coins are dated with a different calendar, like Hebrew coins and Chinese coins.  These preceded our calendar, but so did the calendar of the region.  They can put a coin in a two year spread.  Really, it is a one year span, but it overlaps two of our years.

So, not all coins have dates, and in a few rare cases the dates are not the year of release.

Blaack Spaniel Gallery Coins