When should I remove SID history and remove source accounts from ACL's?
Domain Migration Administrator 7.x
We recommend that you do not remove SID history until you have translated security on all resources that contain references to source accounts. Also, you should have a plan for the Exchange migration (if applicable), as some Exchange migration steps or Exchange 5.5 mailbox access may require SID history.
Refer to Chapter 2 of the DMA User Guide, 'Planning and Performing Your Migration', for a complete check list of the recommended process. We recommend that every migration include testing to ensure the desired results are achieved.