Order by YYYY MM DD in reverse chrono order trouble

Hello,

I am trying to select distinct dates and order them in the reverse
chronological order. Although the column type is TIMESTAMP, in this
case I want only YYYY, MM, and DD back.

I am using the following query, but it's not returning dates back in
the reverse chronological order:

SELECT DISTINCT
date_part('year', uu.add_date), date_part('month', uu.add_date),
date_part('day', uu.add_date)

FROM uus INNER JOIN ui ON uus.user_id=ui.id INNER JOIN uu ON
ui.id=uu.user_id
WHERE uus.x_id=1

ORDER BY
date_part('year', uu.add_date), date_part('month', uu.add_date),
date_part('day', uu.add_date) DESC;

This is what the above query returns:

date_part | date_part | date_part
-----------+-----------+-----------
2004 | 2 | 6
2004 | 4 | 20
(2 rows)

I am trying to get back something like this:
2004 4 20
2004 4 19
2004 2 6
...

My query is obviously wrong, but I can't see the mistake. I was
wondering if anyone else can see it. Just changing DESC to ASC, did
not work.

Thank you!
Otis