While the provided context from SD Bullion and CoinValueChecker indicates the existence of detailed lists of valuable Kennedy half dollars, the specific content of those lists is not supplied. An answer must therefore be synthesized from general numismatic knowledge regarding this coin series.
The value of a Kennedy half dollar is primarily determined by its metallic composition, mintage figures, physical condition or grade, and the presence of any rare errors or special varieties. A definitive ranking can be fluid as market prices and collector demand change, but certain issues consistently stand out as the most valuable.
Among the most prized is the 1964 Special Mint Set (SMS) half dollar. This coin is exceptionally rare, with only about a dozen examples known to exist, and its unique satin-like finish distinguishes it from regular issues. High-grade specimens of this coin are valued in the tens of thousands of dollars, making it a pinnacle for collectors.
Another key date is the 1970-D half dollar. This coin was not released for general circulation and was only available in official mint sets, resulting in a relatively low mintage of just over two million coins. Uncirculated examples command a significant premium. Similarly, the 1996-W issue, struck at the West Point Mint and included only in uncirculated sets to commemorate the 25th anniversary of the clad half dollar, is a modern low-mintage key date.
Silver content provides a baseline value for many early issues. All 1964 half dollars were minted with 90% silver, and coins from 1965 through 1970 contain 40% silver. While common circulated examples are valued primarily for their silver content, specimens in very high mint state condition, such as MS-67 or above, are scarce and can be worth thousands.
Error and variety coins also populate the list of most valuable Kennedy half dollars. The 1974-D Doubled Die Obverse is a prominent example, easily identified by the clear doubling on the motto "IN GOD WE TRUST." Another sought-after variety is the 1982 "No FG" half dollar, which is missing the designer's initials, Frank Gasparro, from the reverse.
Finally, special commemorative issues from the U.S. Mint are inherently valuable. The 2014-W 50th Anniversary Gold Proof Kennedy half dollar, struck in three-quarters of an ounce of pure gold, is one of the most valuable modern issues. Other special releases, such as the 1998-S Matte Finish and various high-grade silver proof coins, are also highly sought after by collectors and contribute to the list of the most valuable coins in the series.
