Previously 'VERSION' parameter of RESTORE command only accepted values starting from 1 up to 99 and sometimes customer want to restore dataset of version higher than 99.
Release: Disk Backup and Restore
To restore other than the most recent version of the data set contained in the Disk archives (an archived or backup copy), specify from -1 to -32767 to get the successively older version of the data set.
For example: VERSION=nnnn
Refer to Disk tech guide for VERSION parameter..