is it possible after so many thousands of coins, that I have finally found an actual error? Or are my eyes just crossed after looking at so many coins?
if you look elsewhere, such as the base of ICA you'll see the same result. Also the flat ring around the edge too showing something is going on with the die ... Don't focus on just one area. Look around. Get a larger picture of what's going on with the coin and the devices.
I'm not really upset at all. I don't truly care if after striking (figures just for example) a million of any one coin (say for example a 1990 P Washington Quarter) that every single one of the remaining ones has noticeable mechanical doubling and extreme die wear that makes every single BU one of the remaining 612,792,000 coming out of the mint virtually noncollectable and not worth more in its lifetime than for spending or getting stuck in dryers. I know that cost-wise, quantity minted in the time allotted is primary, as it should be. Quite honestly, even one million of any coin that has over 600 million minted is more than enough to satisfy coin collectors for their higher quality examples when it gives those the chance to be pulled from circulation or in new rolls. And that is the state of what modern coins are at this time. No use worrying or such, just learn to recognize the bad production for the coin you handle, then throw it in the spend pile. True errors are much more rare.
MD is mechanical doubling. There are a few other names and numerous types of doubling but they are all worthless doubling as it common.
Mechanical doubling, machine doubling, ejection doubling. I thought that they changed the process in the 1990's to cut down on the possibility of a doubled die. And then I read a contrarian article that says the exact opposite. However, I believe if you are to look for doubled dies you are not going to find them on modern coinage. Although, there is a nice one on the 2009 Washington DC quarter reverse, and I am sure some others to look for.
MD, etc is when the machine, through wear, or slippage, etc causes the illusion of "doubling". Remember "quantity" .. these machines are producing 250 to 800 per minute!! Proof coins are done about one every 8 seconds +/- which is 6+ per minute by comparison. Real "doubling" is when in the process of making the "dies" themselves, somethings get stamped again slightly off and creates Doubling. There are actually 8 different classes of Doubling in this regards which is briefly summarized below Class 1, Rotated Class 2, Distorted Hub Doubling Class 3, Design Class 4, Offset Hub Doubling Class 5, Pivoted Class 6, Distended Class 7, Modified Class 8, Tilted There are other errors of course, but they are Die related, such as the old RPM where maintenance is done to a die to reestablish a deep Mint Mark to increase the longevity of the die, and it is reapplied slightly off. Then there the "errors" vs "varieties" as you learn more. Usually the super fast "circulation quality" machines are "horizontal" stamping machines with a rotating force for mechanical pressure, for the fastest process possible. The Proof machines are mostly "vertical" stamping machines with a higher hydraulic pressure for the best quality possible. (from my understanding)
They did change the process from multi-squeeze die hubbing to single squeeze process in order to speed things up and updated ( computer controlled engraving devices) ,but there so much chatter and movement ( mechanical process) that the mechanical movement was deemed by the industry to be mint caused rather than mechanical doubling. Thus it became double die also. And I have to add to Clawcoins 8 classes of 'doubled dies' ~~ Class IX God Only Knows ( DD) as per Wexlers and Flynn's " The Authoritative Reference on Lincoln Cents (2nd) 2009. So I guess any coin from the single squeeze era ( still continuing), the definition of a doubled die is in the mind of the beholder ( seller and/or TPG ). As they said " God Only Knows" . IMO Jim