......as someone who has been involved in countless depositions over several decades I can tell you that when a case goes to the mat (full jury trial, no settlement) those “I don’t knows” you uttered in a deposition months or years earlier could sink your ship. Meaning, YOU LOSE the verdict!
I’ve seen memory-impaired witnesses suddenly experience remarkable mental clarity as the cross examining attorney begins marching toward the stand with their deposition transcript in hand. I’ve also seen one simply invent a new lie on the spot, but by that point we already knew were going to win anyway.