From the Heritage Galleries Auction Listing:
1822 25C 25/50C MS66 NGC. Ex: Eliasberg. B-2, High R.5. Apparently the Finest Known of this extremely popular variety coming in a notch above two Gem MS65 coins reported, one by PCGS, the other by NGC. The toning is a delight to behold for any experienced collector with lilac-gray throughout mixed with splashes of blue and yellow-gold near the devices. Many of the silver coins from the Eliasberg Collection had toning that matched this present coin as they were stored in the same type of holders and environment for decades. The devices are frosty while the fields show prooflike reflectivity except for a small satiny area before Liberty’s neck surrounding a small nick. It is all but certain that this coin was struck soon after the handful of proofs were made from this pair of dies, as the present coin is an early die state and shows so many of the characteristics of a proof. Walter Breen considered this particular coin to be a proof, others a business strike. As to the strike, the central devices and legends are sharp save for the uppermost portions of the talons on the eagle, and the obverse stars generally lack their radial lines except for star 10 which is sharp, matching the characteristics of the proofs from this die pairing.
This is one of the most famous engraving errors in American numismatics. The die engraver used the denomination punches for half dollar, and first engraved 50 C. instead of 25 C. Realizing the mistake, he corrected this by engraving the correct 25 over the 50, but he first placed the 5 punch way too low on the die, with the loop of the 5 into the dentils. The 5 punch was moved into proper position, and the denomination was finally corrected. Breen suspects that ailing Robert Scot was the engraver of this blundered die, and this conjecture would fit the evidence. A question comes to mind as to why this reverse die was employed to coin proofs for the year--especially when proofs are known of the perfect die 1822 quarter. Were these blundered die proofs struck first, or later when additional proofs were needed? Both share the same obverse die, perhaps the new perfect reverse die was not prepared until after the initial proofs were struck using the blundered die. The answer lies in careful study of the few proofs from each die pairing, to figure out which came first based on the condition of the obverse die. What is known, is that the 25/50 blundered reverse die has proven to be one of the most coveted of the Capped Bust quarters. Remarkably, the Philadelphia Mint shelved this die after the small issue of proofs and general circulation strikes in 1822, only to resurrect this same reverse and strike more quarters with it in 1828.