|early print-on-demand system|
Do you need to register at all? Start with the principle that both versions are protected under copyright law and registration is not required to obtain rights. Registration is encouraged because it provides some benefits most of which are important if you must sue someone. Because few people have seen the P.O.D. version and nobody has yet to see your new version, you may not need to be concerned with infringement ... that is, until you distribute your revised version.
If you do register ... The Copyright Office views your revised work as a derivative of the P.O.D. work and therefore your registration is intended to provide protection for your modifications. When you complete the limitations section of your application, you would fill it out as shown below:
By the way dept. You would not file a "continuation." We think you're applying the patent definition of that term. Under copyright law a continuation sheet is used to provide additional information that doesn't fit within the original paper application.