Last month my highest number of no-sellers would have been Fotolia by a far shot, but I've started deleting from the bottom. I've left a few of the newer ones with no sales. Still on the fence if I am staying so I've left sellers and new.
Not 100% accurate for SS, but if you go to the 25 per day tab it shows 20 photos per page - multiply 20 by the number of pages, adjust for the number on last page. My number is very close to my port size. Removed images sold are likely still in the sold list, might play small factor.