Vaulted items exported different from number listed

I exported a user's vault to PST using a date range, for example 8/1/2009 to 12/31/2011. The export process reported that there were 74519 items to export. When the export was completed, it reported 1 failed item and 65336 succeeded. Why such a big discrepency? Do these numbers represent virtual versus phsyical data, such with Single Instance Storage, or, did I lose about 9000 items due database corruption or some other problem?

I am running Enterprise Vault 9.0.3 for Exchange 64-bit on Windows 2008 server

Thank you