To be honest, I am a Symantec Backup Exec mover and exactly know, what can be done in a library with different LTO-drive generations. It is possible to declare, what types of LTO media can be used in what kind of LTO drive. Here under Veeam B&R v8 I have an MSL2024 from HP with just an LTO-6 drive. I thought about moving a free LTO-5 drive from another MSL2024 library into my upper mentioned library, which is operated with Veeam B&R v8.
Under Symantec Backup Exec I can decide what LTO-drive can use what kind of LTO-media. The only thing I must avoid, is to inventory all tapes but since we use barcodes, this is no longer necessary. So during the backup jobs, every LTO-drive picks the media, that is allowed for it. Or you can simply partition your backup library.
I know that Veeam's B&R v8 tape library support is not as mature as Symantec's solution, but since you started to support tape-backups from v7, it is still an achievement.
I suppose that reasonably using tape libraries with different LTO-drive generations under Veeam B&R v8 is still a callenge or better said not recommended in my opinion.
Since I don't plan to return to Symantec Backup Exec and use Veeam B&R in future, I have no other choice to patiently wait for new features regarding tape support to come.
I wish Veeam could integrate bar code rules and options for LTO-drives to decide what types of LTO media can be used in this drive.
Using Veeam Backup & Replication 9.5 Update 2 on every backup server here!