A key date coin is simply one of the coins from a particular series which is the most difficult to obtain. This may be the result of an originally low mintage, or the result of a low survival rate which may be the case due to heavy melting or attrition through circulation. Collectors who pursue a complete collection will often work their way through the more common issues of the series and be left looking for one or more key dates. These are usually the most expensive or require the greatest amount of searching.
Ask most people about a rare coin and they will usually mention the 1909-S VDB Lincoln Cent. Generations of collectors have sought and coveted this coin as the key to a complete set of pennies. The reason for the rarity is the low original mintage of 484,000 pieces. These were struck at the San Francisco Mint in the launch of the new design for the series. Following some public attention, the very prominent initials “V.D.B.” on the reverse were removed. Coins without these initials were struck in larger quantities.
Around the time of issue, many people saved examples of the coin due to its high profile nature and well known story about removing initials. This meant that a relatively high number of examples have survived. Despite this, a great deal of demand keeps the premium for the coin high.
Collectors will seek the coin in grades from well circulated to gem, and will be willing to pay a handsome premium to add this famous key date to their collection!