Research sources

United States Mint

• Coin production process
• Die making
• Collecting basics and error coins
• Coin term glossary

NGC

• Mint errors: die-related
• Planchet errors and clip evidence
• Variety versus mint error

PCGS

• Mint errors versus post-mint damage
• Varieties versus mint errors
• CoinFacts error category

Marketplace

eBay’s U.S. Coin Errors category is useful for inventory discovery and comparison, but listing titles and prices are seller-generated. Authentication must come from evidence, recognized references, or qualified specialists.