Minor & Common Errors
In most instance a coin missing a design element is extremely common and caused by a myriad of circumstances. The most common tend to be struck though grease or a mint employee filed it off when removing die clash marks, burrs or attempting to correct other die issues.
Lincoln Cents are known for these issues and are minted in the billions, so most are just common missing elements. Usually a digit is missing of the date or something is wrong with LIBERTY or the motto, since they’re closest to the rim.
Often there was was an issue with adjusting striking pressure on a cent and the O in ONE might be weakly struck at the top, or a digit is extremely weak or missing on a 1943 steel cent, just to name a couple.
A worn die can cause die cracks, chips and make digits and letters look doubled (Poor Man’s Doubled Die) but these are minor and do not add value ot a coin.
Also design elements closest to the rim are subject to other issues with the die being slightly off center causing the L to be further up on the rim, or the die sliding created strike doubling, or die wear that can mimic doubling. So it’s always important to first think of your coin as not a mint error until you learn the coin minting process.
The above nickel a commonly found example and doesn’t have much premium for most mint error collectors.
PMD (Post Mint Damage)
Another reason for issues found on coins is damage from a counter wheel and usually this damage creates parallel lines or parallel lines in a crescent shape on the coin. All of these are post mint damage PMD.
Another coin commonly found is a dryer coin and these coins were tumbled in the dryer process and will have smashed features that make them look thicker or wider than usual.
It is damage and not a mint error. No extra value added.