Copyright years

[Richard Kenner]

    Is there any legal issue behind the copyright years?

Copyrights have an expiration date and the year the work was written (the
"copyright year") is what starts the clock.

    Has it any legal consequences if I've forgot them in my project?

The law changed in this area recently and I believe the answer now is "no, if
you can prove the year by some other method".  But the copyright notice
is the best way to establish copyright.