The following information is from a posting on the U.S. Mint's website:
"First Strike" or "First Release" Designations
Coin dealers and grading services may use these terms in varying ways. Some base their use on the dates appearing on United States Mint product packaging or packing slips, or on the dates of product releases or ceremonial coin strike events. Consumers should carefully review the information below along with each dealer's or grading service's definition of "first strike" or "first release" when considering a purchase of coins with these designations.
The United States Mint has not designated any coins or products as "first strikes" or "first releases," nor do we track the order in which we mint coins during their production. The United States Mint strives to produce coins of consistently high quality throughout the course of production. Our strict quality controls assure that coins of this caliber are produced from each die set throughout its useful life. Our manufacturing facilities use a die set as long as the quality of resulting coins meets United States Mint standards and then replace the dies, continually changing sets throughout the production process. This means that coins may be minted from new die sets at any point and at multiple times while production of a coin is ongoing, not just the first day or at the beginning of production.
United States Mint products are not individually numbered and we do not keep track of the order or date of minting of individual coins. Any dates on shipping boxes are strictly for quality control and accounting purposes at the United States Mint. The date on the box represents the date that the box was packed, verified and sealed, and the date of packaging does not necessarily correlate with the date of manufacture. The date on shipping labels and packing slips for coins that are sent directly to United States Mint customers from our fulfillment center is the date the item was packed and shipped by the fulfillment center. The other numbers on the shipping label and packing slip are used for tracking the order and for quality control.
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