Before the 1970s, primaries were just in a couple of states and were weird (In 1968, only Reagan was on the ballot on the California primary!!!). Reagan was not the only one, Dewey got 100% of Illinois's vote in 1940, Humphrey got 100% of South Dakota's vote in 1960 etc... 1972/1975 was when the modern-day style primaries finally took place in EVERY state, and no one has gotten 100% in a primary since. How can modern-day primaries exist before the 1970s?