A Misplaced Date (MPD) occurs when the die sinker accidentally places the date way out of position. This is different from a repunched date, where a slight misalignment occurs between one or more punches of the date logotype. A Misplaced Date often occurs when the date logotype is dropped accidentally onto the die. In the case of the 1847 Half Eagle, three different MPDs have been discovered thus far, a surprisingly high number for any US coin. The most obvious MPD, and the one listed in the GUIDEBOOK, is known as FS-301 (formerly FS-303). On the FS-301, the top of a 7 can be seen nestled in the denticles below the final 4 and 7 of the date. The other two MPDs are less obvious but no less valuable. On FS-302, a trace of a 1 is evident at the lower front of Liberty's throat. On FS-304, a trace of a 1 is just barely visible on the lower edge of the point of Liberty's bust. The Repunched Date variety (FS-303) should not be confused for an MPD.
As of September 2011, PCGS had certified ten examples of the 1847/7 MPD (FS-301), the finest of which is a single PCGS MS-63.
Sources and/or recommended reading:
"Cherrypickers' Guide to Rare Die Varieties of United States Coins", 4th Edition, Volume II by Bill Fivaz and J.T. Stanton