Enoch,
I think this is more of an Exchange question than a NetBackup question.
You may be able to find information about logs that aren't truncated in the bpbkar log on the master server, but I don't think that's exactly what you're looking for.
Here is a quote from this tech note: http://seer.support.veritas.com/docs/275180.htm
The correct method of backing up the Information Store for Exchange 2000/2003 is to back up the storage groups associated with the Exchange server. The backup should occur at the storage group level. Mailbox and public folder stores are contained in storage groups. Each storage group contains a common set of transaction logs for all stores contained in that particular storage group. Backup at the storage group level allows for all stores to back up within the same job. In order to successfully truncate the transaction logs for each storage group, all stores within the storage group must first have a successful backup (a failure of any store within the storage group backup will fail to truncate the transaction logs). The transaction logs for a storage group will be truncated only after a successful backup of all stores within the storage group.
Looks like all the logs for whichever storage group is backed up are truncated.
