A missing "latest version" of a project management plan indicates weak document control-specifically, inadequate versioning, storage, access control, and change tracking. Improving the configuration management process (A) is the correct preventive action because configuration management governs how project documents and deliverables are identified, versioned, approved, stored, and retrieved. A robust configuration management system ensures there is a single source of truth, audit trails for changes, controlled access, and clear ownership for updates. Registering an issue (B) addresses the symptom but does not prevent recurrence; it is reactive. Keeping lessons learned current (C) is valuable, but it does not directly solve document version control. Reviewing QA processes (D) may help indirectly, but configuration management is the specific discipline that prevents missing or conflicting versions of controlled documents. Strengthening configuration management protects governance, enables reliable change control, and reduces rework and confusion when updates must be made quickly.