Check these sentences, please

Hi. Please help me with these four sentences.

1. From that time on, they dared not talk back at him. -- Whenever I see phrases like "From that time on," my preference for the choice of tense leans toward present perfect (not sure it is correct to do so or not, though). Is the past tense "dared" correct? Could we changed the word "dared" to the word "didn't," would it be correct?

2. For this one, the harmful effect from the substance used since the early 19XXs, is causing long-term ramifications. -- Let us assume that the letters "XX" represent the last two digits of years like 1980 or 1990. As to the questions: Is the sentence correct? Also, would you say what is ellipted before the word "used" is the phrase "that was"?

3. This is being used since the early 19XXs. -- Let us also assume that the letters "XX" represent the last two digits of years like 1980 or 1990. As to the question: Is it correct to use a present continuous tense with phrases like the above "since the early 19XXs"?

4. He told them it would happen. He had read the report and knew it was going to happen. When it happened, they weren't surprised. -- I think the verb "knew" above could be replaced with the verb "had known." Am I correct?