Microsoft Exchange Migration Wizard Problems

We got our two exchange servers that are resident on different forests talking to each other by setting up the 'bridgehead' of the two with a "Forward All Mail with unresolved Recipients to this host: x.x.x.x" setting under SMTP Virtual server properties --> Messaging Tab

Now that mail routing is working between domains/forests we have another problem with the migration of accounts.  Below is the different methods we've used to migrate accounts and the results that we've seen.


Attempt  #1:  ADMT migrate a user, use Exmerge to export from source, use Exmerge to attempt to import unto target account

Result:  Can’t find target mailbox on the destination Exchange server
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Attempt  #2:  ADMT migrate a user, use Exchange Migration Wizard to move them over after setting the “Associated External Account” permission to the Administrator account of the destination forest/domain

Result:  Completes successfully but their mailbox doesn’t show up in the destination exchange server and their Exchange Home Server (under the Exchange General Tab) still is pointing to the old Exchange server resident on the old forest.

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Attempt #3:  Migrate the mailbox & user account with the Exchange Migration Wizard (does them together when it moves the mailbox) and then update groups memberships etc with ADMT.
Result:  Seems to work great.   The problem is that we’ve already migrated a few dozen user accounts.  

Will we have to delete these from the destination domain in order to do the migration in this manner?  Is there an easy way to move mailboxes in this circumstance where we won’t have to redo the initial migrations?