There are two main varieties of the 1974 Kennedy half dollar: the "Type 1" and the "Type 2." The Type 1 has a smaller date and the letters "D" and "P" are closer to the date. The Type 2 has a larger date and the letters "D" and "P" are farther from the date. The Type 2 is more common than the Type 1.
In addition to the condition and variety, the value of a 1974 Kennedy half dollar can also be affected by its mint mark. The 1974 Kennedy half dollar was minted at the Philadelphia Mint (no mint mark), the Denver Mint (D), and the San Francisco Mint (S). The San Francisco Mint 1974 Kennedy half dollar is the most valuable of the three, followed by the Denver Mint 1974 Kennedy half dollar and then the Philadelphia Mint 1974 Kennedy half dollar.