Pour ceux qui ne collectionnent pas les pièces Américaines dont il est fait mention dans l'article, je vous soumet ceci pour peut-etre une plus grande compréhension.
Photo et petit texte anglais. (2007-S dollars Jefferson)
The date, mintmark, and mottoes are applied to the edges of proof Presidential dollars by a three-piece segmented collar that surrounds the coin planchet and simultaneously impresses the incuse edge inscription into the coin while the obverse and reverse dies are striking.

The collars for the proof Presidential dollars are changed frequently. “It is estimated that on average each segmented collar produces 30,000 coins,” said White.
Pour ceux qui veulent lire l'article.
http://numismaticnews.net/article/Where ... on_errors/