This preserves the actual address of the local endpoint for an expired control tunnel, per its description, the historical companion to the live cisgIpsSgTunLocalAddress. It's the concrete value an admin uses to confirm exactly which local interface or address a now-closed tunnel had terminated on, useful on multi-homed devices where multiple local addresses could have hosted the connection. Reviewing this across many history entries can reveal whether tunnels are consistently anchoring on the expected outside address or intermittently using an unexpected one.