JDM 4th Gen Legacy were released in 2003 and they come on US Market a year later in 2004. Facelift were done in middle of 2006 year in Japan, and in 2007 in USA.
So that's why you can eventually see yearly 2006 pre-face and late 2006 facelift JDM Legacies.
Facelift is a minor change in exterior and interior, here's some example of pre-facelift:
And some facelift: