There are at least two ways to maintain an historic sequence of backup files:
Different target directoriess. You can maintain separate target directories for each date's backup. For example, /var/master1_bakup/July14, and /var/master1_bakup/July15, and so on. While this method is simple it wastes disk storage space.
File system backup. The most common method of maintaining an historical sequence of NIS+ backups is to simply include the backup target directory in whatever regular file system backup method that you use. To facilitate this, the nisbackup command can be run from a crontab file, or from within the Solstice backup routine. See your Solstice documentation for information on how to specify that commands like nisbackup be automatically run as part of the system backup procedure.