"We're Going Home..."
It is safe to say that Cooper retained all of his previous knowledge of the events on 02/23/1989 because:
1. He solved the murder.
2. He asked to be placed there that night to save Laura from her Fate.
So WHY on earth would he take her home to a murdering, raping Father?
Guess what? Bob would still be alive and well inside of Leland if you go back to a time before he left Leland's body.
It's simple time travel 101...