i would like to add some more to this!
warrior cats are
extended releases, which means
they don't always have an adoption date that matches their archive placement!as long as it isn't from december 18th or december 11th 2014 it's a true-date and not a re-release :]
for example,
this leafpool is adopted in january 2010 and
this one is adopted in october 2009. both of them are adopted months way after february, which was leafpool's original release date - but are still considered true dates due to their extended release time. this goes for every warrior cat, as far as i am aware!
but yes, in the archive all warrior cats are in 2008-2009 - outside of events.