Thanks again, I missed all the talk about Pool Numbers so don't know how the work I have looked through the help files on the system but they are not very clear.
What I have managed to do which I think will work. When I imported the file I set a source as the person that sent it to me so I ran a query on links to that source and have come up with over 200 names.
I think I am going to admit defeat and just leave them in my tree for the time being.