Thanks Liam,
Problem with xcopy was it was a new DC, new everything, so even if I had I don't think the security identifiers would have married up on the new system even if the student id's were created the same, I might be wrong on that.
I have been chasing my tail on some snap decisions I made during that dark time in September that's for sure, in hindsight I should have just told the bosses what they expected wasn't possible on that timescale and took my lumps.