Is there one person in your organization who serves unofficially as your “historian” or “librarian”? These people typically have worked for many years and are the holders of your institutional knowledge.
They know how you did things 15 years ago and how and why processes changed over time. They remember your company superstars and what they contributed. They recall the good and bad managers, and the impact they had on the staff.
They know things about clients that are tucked away in the back of their heads, only to rise to the surface if something related to those clients appears.