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.
A very small group of Proof errors recently came from a collection that was auctioned by the State of California. 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 it has been dispersed since the sale.
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.
Proof Errors are featured in the NLG award
winning book, World's Greatest Mint Errors.