you should put the number of plates we are bidding on in the description. 12 is a lot for one auction and you may not get the credits they are worth. I would have had 3 listings of 4 plates. The better you describe the item the better they will do
I think you can edit after you have bids but I am not sure. If you cannot edit after bids you can confirm it in the comments. If you say definitely you are bidding on 10 plates or 4 plates or whatever # you will definitely get more bids. Hope this helps.