Hi Scott,
FYI,
The syslog messages have a sequence number attached. If the Monitoring and Report Viewer goes down or if it is not able to receive messages from ACS, then the Monitoring and Report Viewer retries those missed logs from ACS, using the logging recovery mechanism.
The Monitoring and Report Viewer processes the syslog messages, and identifies any discrepancies in the sequence. In this way, it finds the messages that have been missed.
The Monitoring and Report Viewer then notifies the ACS server to resend the missing log messages. ACS server processes the messages stored in its local store and resends them to the Monitoring and Report Viewer.
For the Recovering Log Messages feature to work as desired, you must enable the Log to Local Target option for the relevant logging categories in ACS under System Administration > Configuration > Log Configuration > Logging Categories > Global.
To enable Recovering Log Messages, from the Monitoring and Report Viewer, select Monitoring Configuration > System Operations > Log Message Recovery.
For more detail, please go through the following link:
http://www.cisco.com/c/en/us/td/docs/net_mgmt/cisco_secure_access_control_system/5-5/user/guide/acsuserguide/viewer_sys_ops.html#wp1052728