Store responsibility, not just names
For each process, record the owner, backup, scope, decisions they can make, and the source of authority. A contact list is weak when nobody knows what to ask each person.
Check it against live work
Use recent escalations and returned requests to find stale or ambiguous ownership. Update the directory when work moves teams, not only during an annual cleanup.
Protect the directory
Limit sensitive contact detail to the people who need it and keep an effective date. When nobody accepts a process, raise the gap to management instead of assigning authority by default.