Pages has never been a Word clone and opening a Word document introduces a translation process that transforms into Pages internal document format. The original Word document is unscathed and uneditable in Pages. Translating the Pages document back to Word document format is another translation process. Apple does not guarantee any accuracy in that translation.
Word 97 was also numbered Word 7 and if your versioning is correct and the conversion to Pages occurred before October 2013, then it was opened and translated in (probably) Pages '08 or Pages '09 on Mac. That may have introduced font substitution and would have dropped unsupported Word features. It may have introduced other Pages proprietary changes to the converted document that did not save or export back to Word properly.
When Apple retired the older Pages 'YY applications, it completely rewrote Pages without basing it on the older Pages source code. This not only dropped nearly a hundred features previously in the older Pages, but also introduced a new Pages document format. As a consequence, some of the Pages 'YY templates could not be converted to the newer Pages template format, and some features in the older Pages were dropped when opened in newer Pages applications after Fall 2013.
The correct management of Word documents is to keep them in their native document format by opening, editing, and saving them again using Microsoft Word.
