It was a one a day habit at least during that period so 300 a year might be underestimated rather than over. My database with most of the write ups from the past 4 years has over 1100 films in it. I don't have the time (or inclination) anymore so the most productive period I had was for about 3 years. I used to come home from work mid morning, sleep, cycle mid afternoon and watch a film late afternoon. So you need a steady routine to make this work.
If I found a director, like Godard or Wong Kar Wai, I didn't like , I would still give them 3 films, but no more.