This holds true in my case because before 1978 my residual memories are very few and far between. The memories don't start piling up in earnest until around the time I turned four and afterwards (the fall of 1978 forwards). After I turned four it quickly becomes a torrent of memories leading into my first days in school and so forth. I have very vivid and plentiful memories of the first Superman movie, ST:TMP, The Empire Strikes Back
and the 1980 presidential election, and all four happened between age four and my sixth birthday.