Copyright year is 2006 about google-diff-match-patch HOT 1 CLOSED

That's a good question.  Google's policy for source code is to record the year 
of
each file's creation, then leave the date unchanged when making updates.  This 
is the
most conservative approach, allowing the copyright to expire sooner.

Some companies increment the copyright every year in order to maintain a claim 
for
perpetual copyright.  Other companies maintain a date range for each file, 
though
this can get complicated:
http://www.nntp.perl.org/group/perl.perl5.porters/2003/03/msg72648.html