The CSS file after export contains identical classes for each file within the Book document, distinguished by an added integer corresponding to file sequence, so that:
will be followed by all style tags created from first file, then
will occur in the CSS, and correspond to a new style tag created from the second document in the book file, ("File02.indd"), within the conversion file, "File02.XHTML", although the style utilized is the same as used in the first document, ie, "File01.indd".
The consequence of this is a CSS file with some thirty classes for every style tag shared by all of the files contained within the book.
All of the styles are applied cleanly, without any overrides.
The solution points to how, it appears, the book panel export is functioning: each file exports a set of tags referenced to itself; file01 adds a "1" to its tags, and so forth. What I was able to do was use a file referencing all of the tags in the style suite in two ways:
Also, applauds to "celkins" at InDesignSecrets.com for both the description of her problem and her solution, which confirmed, for me, that my "experimental" process was the right path, and perhaps, the best path to a solution.