Better Validation of year

I have a minor request: The Year-Validation has a problem - as publishers use to use the next year as a publishing date, if a book is published just at the end of the year. For example we have one book to be published this year - 2007 - but the official publishing date is 2008. Therefore it should be possible to enter the next year for maximum.

I changed this line of code, adding a +1:

elseif ($node->biblio_year < 1 || $node->biblio_year > $today['year']+1)      form_set_error('biblio_year', t('Year of Publication must be a number between 1 and ') . $today['year']+1);

no - i am asking myself - as a second proposal - to have something like "unknown" as an option for year...

regards
Christian