I though this has been brought up before and put to bed. My understanding is and I may be wrong. I though it came down from Admin.
1. Base set of stickers with all the back Var we found and verified for sure. A lot of time from many members to do this set. There have been Var that appears that the sticker was removed and replaced with another sticker that members wanted to add. There was a few on COMC at the time and was removed when told that you could see the stickers were not on correctly. I asked them to remove or verify several of them. They removed them.
2. Set of all the backs with no stickers on them. This set was added as they were printed on the card stock. Approved by Admin. I may be wrong but to me the only way to get them was to remove the stickers from the front. I never got an answer when I ask the question if they were sold with a blank back.
3. The so called "Proofs" were missing a step in the process from everything that has been looked into. As there is no real way to figure out if they are really proofs or just someone who is selling them as proofs. Again, I though COMC reply about this was that was the way of showing that there was a different between the stickers.
Way too many people are selling processing/printing errors as rare and valuable cards.