I've got the same problem as StephenO2. Everything was going like clockwork — I held down the alt key on my Mac whilst opening iTunes, Chose Library and the Get Info key shows me the track is still in its original place after I selected the External Hard Drive as the destination of the new Library. Fingers crossed you can bring closure....
I've been thinking about doing this for a while to keep the storage almost full notice at bay. Why Apple sell us laptops with so little space I've no idea.