You want "score FH_DATE_PAST_20XX 0".
SpamAssassin gives any message sent in 2010 a default score of 3.2 because that date "is grossly in the future." But it gets better: they discovered and "fixed" this in June 2009... but never bothered to push out a release. Because being fixed in CVS is good enough, right? That's the Linux way.
Current Music: Course of Empire -- Coming of the Century ♬