My educated guess (as a specialist on euro coins with errors) before seeing a picture is that there was some dirt on the die when the coin was struck. If I'm right, the place where the year should be, is somewhat deeper than the rest of the coin and with an uneven surface.
There is most likely a (small) series of these coins in circulation. Such errors are not rare, but quite nice nevertheless. I have a variety of them in my own collection, the most severe hardly recognizable as a Dutch coin.
Greetings,
Senior
Do you have information about euro variants? Tell me!