Long considered the key date in the set, the 1856 Flying Eagle holds legendary status among coin collectors for its overall popularity. Business strikes of this issue are somewhat controversial, as some experts consder all 1856 Flying Eagle cents to be struck in proof format, even if the mirror finish isn't pronounced. Rick Snow, noted author and researcher of the series, has stated in his reference book that only two die varieties (S-3 & S-9) are to be considered as business strikes.