Proof coins are struck by technicians who hand feed the blanks into special presses. They are produced, examined and packaged using extreme quality control. It is very unusual to find major proof errors. A few broadstrikes, off-centers, double strikes (in collar) and off-metals have been known to be found in sealed proof sets. Proof errors are aggressively sought after by many error collectors.
This unique pair of PROOF 1969-S Roosevelt Dimes were struck together and mate perfectly. The first coin was double-struck off-center and fits perfectly into the second coin, which is an incuse-brockage. It's amazing that both survived the minting process and were kept intact and in gem proof condition. As mentioned above, this proof mated pair was originally discovered in a group of San Francisco proof mint errors that was auctioned by the State of California. This unique mated pair was certified by NGC and Coin #2 is in a holder with double-thickness since it was double struck at such a severe angle.
This is one of the most dramatic, fascinating and intriguing proof errors ever discovered. Certainly this unique mated pair of proof Roosevelt Dimes ranks at the top of all mint errors known. The size, eye appeal, and visual effect of being struck together is amazing. In addition, the status and prestige of being struck in proof makes this pair one of my favorite mint errors in 40 years of handling numismatic rarities.
Coin #2 is in a holder with double-thickness
since it was double struck at such a severe angle.
Exotic and Intentional U.S. Error Coins In The Marketplace
One of the most controversial categories of U.S. coins are mint errors. Many dealers and collectors, as well as coin auction houses, buy, sell, trade and auction many rare, exotic and unique major mint errors. Obviously, some of these defy logic and were intentionally created and taken out of the Mint.
In the early 2000's, a group of several hundred U.S. error coins were found in a safe-deposit box. Fred Weinberg purchased this group which included coins struck for proof sets and also coins struck for circulation. This group was auctioned by the California State Controller's Office of Unclaimed Property. The U.S. Secret Service inspected and released this collection to the State of California determining that it was legal to own. The State of California then auctioned the collection and the rest is history.
Another example of U.S. error coins escaping the Mint occurred in the 1970's. A hoard of proof error coins were smuggled out of the San Francisco Mint inside the oil pans of forklifts that were being serviced outside of the Mint. This topic was discussed in the June 6, 2022 Issue of Coin World, which covered Fred Weinberg's account of this story. The Coin World Managing Editor concluded:
Obviously, the marketplace accepts these coins, and some collectors are happy paying thousands of dollars for coins that show every indication of having been created through illegal means.
In Episode 11 of the PCGS video series Slab Lab, Seth Chandler interviews Fred Weinberg. In part 2 of the interview, Fred explains in detail why mint errors that are decades old are not recovered by the U.S. Mint. Fred's recollection of conversations in his office with the Chief of the U.S. Mint Police are extremely insightful and explain why the Mint doesn't attempt to recover error coins from decades ago.
Proof Errors are featured in the NLG award
winning book, World's Greatest Mint Errors.