I'm going to be re-issuing one of my non-fiction titles, to add additional material. There's no question that it will be a new edition, so that means a new ISBN. However, I had to cut some explanatory information from the first edition to keep it under Amazon's page count limit. With the new material, I'll definitely be over. That means I'm looking at two volumes -- which will also allow me to restore the content I had to eliminate from the first edition. Am I correct that each volume of the new edition has to have its own ISBN?