When was the last time that the Democratic candidate was not already known before the National Convention?

Question

I was watching last night as they went through the roll call of States, but the outcome had already been decided so it was just for show. When was the last time that the nominee had not already been chosen (if not ratified) before the DNC?

Answer 1

One could say 1968, when Humphrey attained the nomination due to Robert Kennedy's assassination, and during the fiasco which surrounded the DNC in Chicago.

But the better answer is 1952, when it took three ballots for Adlai Stevenson to be chosen.

Answer 2

1952.