There are major change in product from 7.1 to 8.1.2. To jump on 8.1.2 is not advisable.
"The NetBackup 8.1 upgrade guide provides an upgrade path from NetBackup version 7.7.x through 8.0. If you want to upgrade from NetBackup versions older than 7.7.x, you must first upgrade to NetBackup 7.7.x or NetBackup 8.0. Then you can complete your upgrade to 8.1 with the 8.1 upgrade guide."