server_log server_x -a -s is all of server:log data you will get.  Older server:log data is not available because it is already overwritten. There is no log rotation for server_log, the standard linux log trimmer/rotation is not working for server:log, because server_log is not stored in a file, but a partition on disk.  Your only chance is using other log files, f.e. syslog, cmd_log ....  If the datamover is failed over, maybe a server_log against the failed server will be of help.  For the future your client need to ask earlier or you need to install some script which will archieve the server_log.
I have a client that is asking if there were any "nas" related issues on a certain date.  Porblem is when I run server_log server_2 it only gives me so many days.  Is there any other logs that would give me older info?  EX:  [nasadmin[NAME] nas]$ server_log server_2 -a -s | more NAS LOG for slot 2: -------------------- 2012-08-02 19:53:10: ADMIN: 6: Command succeeded:  volume hyper 4895 1 4894 2012-08-02 19:53:10: ADMIN: 6: Command succeeded:  volume slice 4896 43810816 40960000 4007  They want data from 2012-07-25  Thanks!
Historical server_log data