ASC and DESC in SQL query not producing different results

I have a custom query that works but I want to reverse the order. For some reason, changing ASC to DESC doesn’t seem to make a difference. Here is the SQL:

SELECT wposts.*
FROM $wpdb->posts wposts, $wpdb->postmeta wpostmeta
WHERE wposts.ID = wpostmeta.post_id
AND wpostmeta.meta_key = 'Date'
AND wposts.post_status = 'publish'
AND wposts.post_type = 'post'
AND wposts.post_date < NOW()
ORDER BY MID(wpostmeta.meta_value,7,10), MID(wpostmeta.meta_value,1,2), MID(wpostmeta.meta_value,4,5) DESC

The custom field contains date in mm/dd/yyyy format, and I’m sorting the results initially by using the MID function on the value (so it sorts by year, then month, then day). The results come out in order from oldest to newest. Swapping ASC and DESC doesn’t change the order. Any/All help much appreciated.