Well you have an Enterprise Vault Archive, which is associated with your Exchange Mailbox.
Whenever a change is made to your policies or archives etc, you need to perform a synchronization against the exchange mailbox
this will update the hidden message with any new policy settings etc.
In this case what might be happening is that your hidden message in your mailbox references all your old archives etc
so on the Archiving task which looks after your mailbox, if you go to the properties, you have a synchronization tab to which you can choose your mailbox to give it the latest policy settings etc and update archive ID's and what nots
Note that synchronization should occur once a day, and can run twice a day if configured
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