2.1.260 Part 1 Section 17.8, Fonts

a.   The standard states that when a font is unavailable, font substitution elements may not be modified.

Word can modify the font substitution elements (altName, panose1, charset, family, notTrueType, pitch, sig) if a font with the same name has been loaded before in the same application session.

b.   The standard does not state that different forms of embedded font types must be from the same font.

Word can only display one embedded font per font name.  If embedRegular ("[ISO/IEC-29500-1] §; embedRegular"), embedBold (“"[ISO/IEC-29500-1] §; embedBold"), embedItalic (“"[ISO/IEC-29500-1] §; embedItalic") or embedBoldItalic (“"[ISO/IEC-29500-1] §; embedBoldItalic") specify different fonts, only one of these fonts will be used to display all variations. If multiple documents are loaded which specify different embedded fonts for a given font name, only one embedded font will be used to display all variations of such font across all documents.  When Word saves a document; embedRegular, embedBold, embedItalic and embedBoldItalic will all be embedded forms of the same font.