By default, task history for the Symantec Management Agent (SMA) is kept for the tasks from last 90 days. You can configure that period for the 7.5 SMA by adding a new key to the Windows Registry on the managed computer.
To configure the agent's task history purging period:
Note: The purging period can be set to 0. If you set the DWORD value to 0, the task history is not kept.