United States Bicentennial coinage carried the dual date 1776–1976.
The United States Mint placed the paired dates on the Washington quarter, Kennedy half dollar, and Eisenhower dollar to connect the nation’s founding year with the 200th anniversary year. These coins were circulating commemoratives rather than purely collectible medals.
The coins were struck during both 1975 and 1976, but none carried a single 1975 date. That production detail often causes confusion: the manufacturing year and the commemorative date are not the same thing.
The coin designs also differed by denomination. The quarter showed a colonial drummer, the half dollar featured Independence Hall, and the dollar showed the Liberty Bell superimposed on the Moon. This question concerns the shared date, not any individual reverse image.