I am at a crossroads of upgrading my Veeam Backup environment from v6.5 to v9 and just found out through Veeam support (case 01741886) that none of my existing 6.5 Veeam backups will be able to be restored by Veeam v9. For some reason, Veeam made the decision that they would only allow restores from 2 previous versions, yet allow you to archive to tape and keep backups indefinitely. The support staff told me I would need to keep a viable 6.5 Veeam server running or a copy of the installation ISO to be able to set up a 6.5 server to be able to restore from backups that I am making up to the day I switch to v9.
I would like Veeam to look into allowing their S/W to be fully backwards compatible with all versions. It makes no sense to be able to archive to tape if you can't restore the Veeam backup files that are pulled back off the tape in the version you are running.