The year 1776 marks the official beginning of the United States of America's nationhood. The year 1976, as the 200 year anniversary, was a big year for coins, including the Eisenhower Dollar.
The Eisenhower Dollar was manufactured in 1975 and 1976, with all "Ike Dollars" bearing the 1976 date (there are no Eisenhower Dollars with the year 1975). There is a way to tell which coins were manufactured in 1975 and which in 1976. The reverse of the coins made in 1975 coin is different from the coins made in 1976. The lettering on the reverse of the 1975 coin is "thick", and the lettering on the 1976 coins is "thin". See the photos below for examples:
Here is an example of the coins made in 1975 (Variety 1 or Type 1)
And here is an example of the coins made in 1976 (Variety 2 or Type 2