While it is factually correct that Reagan was elected in 1980, he announced his candidacy a year earlier in... wait for it... 1979.
And again, while the "Reagan Era" is usually designated to have begun with his election, the origins of the ideology and historical time period that bears his name began in the 1970s
He was very much a product of the school of thought that bears his name. As a charismatic face, he made a great figurehead, but he didn't invent the thoughts.
I don't question the choice of the anthologist of World War 3 Illustrated to go back to 1979 for the beginning date.