Closed Vault Partitions - Backup advice

EV 10.0.3

Win Server 2008R2

Backup Exec 12.5

We have over 4TB of Archives that are currently in Closed Vault Partitions, we currently backup weekly these along with the Open Partition.

Is there any reason we can't just backup the Open Partitions weekly and the Closed ones on a less frequent cycle, Monthly for instance or even 6 monthly. We do use CAB Collections and users can delete items from their Archive

Thanks

Jon