TSM v4.1 for AIX, Administrator's Guide, Table 27 (Table 22 in Windows
guide, Table 26 for Solaris)
"NOLIMIT/NOLIMIT        60 days/180 days
Retain Extra Versions controls expiration of the versions. The server does
not expire inactive versions based on the maximum number of backup copies.
The inactive versions (other than the last remaining version) are expired
when they have been inactive for 60 days.
If the user deletes the REPORT.TXT file from the client node, the server
notes the deletion at the next full incremental backup of the client node.