Howard,

We were carving out a division of our company to its own new company.
We used DMA to migrate their accounts.
After migrating, I am running a small project to clean up the systems of traces of their accounts/groups/etc.
I suppose my manager was thinking there could be deleted accounts in the source domain that now show up as SID's. After talking this through, though, it sounds hard to believe or not well thought out. I did spend about 2 full days working on this script though. I guess I can chalk it up to learning.
Hope this helps.