I think I can answer some of your questions.

>   o What Retention policy gets assigned to a Class backup
>     - the value set under Backup-Policy?
>     - the value set under the Automatic-Policy?
Based on our experience, it is the value under the Backup Policy.  The
value under Automatic does not seem to apply.

>   o Is it possible to create a single class which has multiple
>     Retention policies determined by which schedule is run?
Yes.  The date and time of the backup determines which backup policy
applies.

>   o Can anyone provide an overview of how the Backup Policy Retention     
> Value is used by NetBackup?
I would also like to see this documented more clearly.

--
Deron Johnson
mailto:djohnson AT amgen DOT com