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How can I know when exactly the decade of M&A start?
How am I suppose to interpret the "mid 90s"?
Did the first 1984 survey start before or after the crisis? How am i suppose to know this?

mid 80's/90's is defined for you in the stimulus; they use 1984/94 so it should be interpreted that way. However, it doesn't really matter.
As for your third question, the crisis was occurring in the mid 80s so the survey in 1984 had to have been given after. If it was given before the crisis the argument would not make any sense.