The Log Archive Server will groom data out that is older than the retention period set in the Log Archive Configuration Utility. However, if the data that is older than the grooming period has not been backed up or if Security Manager thinks it has not been backed up, then it will not be groomed.
Most backup utilities will uncheck an advanced NTFS setting. This setting is named "Folder is ready for archiving", but also may be referred to as "the archive bit".
This is an advanced NTFS setting that will be unchecked once a the file/folder is backed up. If your data is not being groomed, please investigate whether your backup utility is setting this advanced NTFS setting with your Backup Administrator.