The key element is when did you get the Dec 2004 wages? If you got them in 2004, then they should be claimed on the 2004 return. If you got them in 2005, then you must claim them on your 2005 tax return.
Look at the W-2 for the Dec 2004 wages. Is it for 2004 or 2005? If 2005, then you must file for 2005. If 2004, then an amended return is in order.