De-duplication does not allow Google to know http://marketing.example.com/tracking/some_user.png in cache is identical to http://marketing.example.co

De-duplication does not allow Google to know http://marketing.example.com/tracking/some_user.png in cache is identical to http://marketing.example.com/tracking/some_other_user.png without passing the second URL — a.k.a. the tracking data — to marketing.example.com.