Some coins struck at the Denver Mint for 2015 Uncirculated Mint sets have what at least one grading service calls “Prooflike” surfaces, with some of these coins selling for premiums at auctions.
The Prooflike surfaces apparently result from environmental conditions at the Denver Mint and the subsequent handling of the coins. Coins struck for the same sets at the Philadelphia Mint are produced under different environmental conditions, resulting in more typical Uncirculated finishes.
Numismatic Guaranty Corp. has graded and encapsulated a number of 2015-D coins with the PL (for “Prooflike”) designation on the grading label. The coins include Lincoln cents, Roosevelt dimes, Kennedy half dollars, and Dwight D. Eisenhower Presidential dollars, according to NGC Vice President Scott Schechter.
The Prooflike designation has not been used thus far for any of the Philadelphia Mint coins in the sets, according to Schechter. The coins certified as “Prooflike” by NGC were extracted from 2015 Uncirculated Mint sets submitted in their original Mint packaging, according to Schechter.
The certified Prooflike Denver Mint strikes coins are garnering premiums on the secondary market, primarily in eBay auctions. One NGC MS-68PL red 2015-D Lincoln cent sold Aug. 30 for $328.33.
Modern U.S. Prooflike coins are typically Uncirculated strikes that exhibit surface characteristics similar to regular mirrored Proof coins. Proof coins are struck under more exacting processes to achieve the Proof finishes.
Collectors Gerald Higgs and David St. Thomas independently noticed the differences in the quality of the Denver Mint strikes compared to the Philadelphia Mint strikes in the 2015 Uncirculated Mint sets each received. St. Thomas’ attention was drawn to the Roosevelt dime while Higgs’ was attracted to the five Presidential and Native American dollar coins in the set.
Higgs wondered how the Denver Mint coins gained the unusual finishes and asked Coin World whether enhanced planchet quality, adjusted striking pressures or modified handling procedures for its collector products was responsible.
U.S. Mint officials provided Coin World the following explanation:
“The Denver and Philadelphia plants have a few factors that contribute to some slight variation in products.