Is a new box of pennies really all 2012's ?

In about a month or so, boxes of 2012's should start showing up which can probably be flipped for a nice profit for those lucky enough to get them early. But how can you be certain that a sealed box has nothing but new uncirculated 2012 pennies in it? Do some boxes come straight from the mint with identifying marks to ensure that they are all from a new batch? I have never seen any boxes like that but I have picked up boxes filled with machine wrapped rolls that sure look like they are solid 2011-D rolls. Without cracking open every roll and checking every coin, can you be certain that no coins from prior years are mixed in?
Do buyers and sellers of these boxes just assume that they are 100% new uncirculated pennies? If all but two pennies in a box are what was expected, that's still a 99.9% accuracy. Maybe that's good enough. Maybe the exceptions are even less frequent than two per box. Does anyone here have first hand experience where a buyer of such a box happens upon that single unexpected penny among the rest? I would sure hate to be on the selling end on eBay where a buyer tried to get a refund after finding one bad penny hidden somewhere inside one of the rolls.
I decided to take a closer look at four boxes that I suspected where solid 2011-D's that where among the boxes I picked up last month. My results were mixed.
Box #1 - Box of machine wrapped rolls in plain brown paper wraps. A quick inspection through the holes in the top of the box showed only shiny new shield reverses or 2011-D dates on the few rolls where I could peek through the holes and past the crimped paper to see a full date. I opened the box to individually weigh each roll. The first 49 rolls weighed in at a little over 126 grams each (50 x 2.5 grams for the pennies plus a little more than one gram for the wrapper). But the last one revealed that my box was not pure. It had a 2006-D showing on one end and it weighed about 127.5 grams. The extra weight suggests that there were two coppers in the roll. The 2006-D on the end has me wondering how many other assorted zincs are mixed in that roll or even the other 49 rolls.
Box #2 - Just like #1 in appearance. Checked both ends of each roll and saw nothing but shields and 2011-D's. So far so good. After weighing all of the rolls there were three in the 127 to 128 gram range. That's extra weight from coppers inside. Another less than perfect box.
Box #3 - Same type as the first two. Two of the rolls weighed in around 123.5 grams. I suspect those only had 49 pennies in them. Four other rolls were slightly overweight with the worst being no more than 128.5 grams. It was the worst box of the three. It's a "mostly 2011-D" box but I wouldn't want to be the guy with an auction like that on eBay.
Box #4 - This one was all String & Sons wrapped rolls - the white paper with red at the ends. All rolls weighed in very close to 126 grams. The crimped ends of the rolls covered more of the surface of the coins on the ends so I didn't see the entire date on many of the coins on the ends. Of all the boxes, I would say this is the only one I would call a 2011-D box and that I would attempt to sell as such if there was still a marked for the 2011-D's.
I don't know which company rolls the coins from the first three boxes - the ones wrapped in the plain brown papper. But I would say that boxes coming from that source are not something that I would try to sell as solid 2011's (or 2012's). I also noticed that the machine they used to do their wrapping left scratches on the face of many of the coins on the ends. So even if the boxes were consistently solid 2011-D's, the damaged coins could be problem for a potential buyer.
Do buyers and sellers of these boxes just assume that they are 100% new uncirculated pennies? If all but two pennies in a box are what was expected, that's still a 99.9% accuracy. Maybe that's good enough. Maybe the exceptions are even less frequent than two per box. Does anyone here have first hand experience where a buyer of such a box happens upon that single unexpected penny among the rest? I would sure hate to be on the selling end on eBay where a buyer tried to get a refund after finding one bad penny hidden somewhere inside one of the rolls.
I decided to take a closer look at four boxes that I suspected where solid 2011-D's that where among the boxes I picked up last month. My results were mixed.
Box #1 - Box of machine wrapped rolls in plain brown paper wraps. A quick inspection through the holes in the top of the box showed only shiny new shield reverses or 2011-D dates on the few rolls where I could peek through the holes and past the crimped paper to see a full date. I opened the box to individually weigh each roll. The first 49 rolls weighed in at a little over 126 grams each (50 x 2.5 grams for the pennies plus a little more than one gram for the wrapper). But the last one revealed that my box was not pure. It had a 2006-D showing on one end and it weighed about 127.5 grams. The extra weight suggests that there were two coppers in the roll. The 2006-D on the end has me wondering how many other assorted zincs are mixed in that roll or even the other 49 rolls.
Box #2 - Just like #1 in appearance. Checked both ends of each roll and saw nothing but shields and 2011-D's. So far so good. After weighing all of the rolls there were three in the 127 to 128 gram range. That's extra weight from coppers inside. Another less than perfect box.
Box #3 - Same type as the first two. Two of the rolls weighed in around 123.5 grams. I suspect those only had 49 pennies in them. Four other rolls were slightly overweight with the worst being no more than 128.5 grams. It was the worst box of the three. It's a "mostly 2011-D" box but I wouldn't want to be the guy with an auction like that on eBay.
Box #4 - This one was all String & Sons wrapped rolls - the white paper with red at the ends. All rolls weighed in very close to 126 grams. The crimped ends of the rolls covered more of the surface of the coins on the ends so I didn't see the entire date on many of the coins on the ends. Of all the boxes, I would say this is the only one I would call a 2011-D box and that I would attempt to sell as such if there was still a marked for the 2011-D's.
I don't know which company rolls the coins from the first three boxes - the ones wrapped in the plain brown papper. But I would say that boxes coming from that source are not something that I would try to sell as solid 2011's (or 2012's). I also noticed that the machine they used to do their wrapping left scratches on the face of many of the coins on the ends. So even if the boxes were consistently solid 2011-D's, the damaged coins could be problem for a potential buyer.