1. if AdvWidthMap/AdvHeightMap missing, deltas for unused (emptied) glyphs are zeroed 2. If indexMap exists and unused glyph ID <= last used glyph ID, then its major/minor number set to 0/0 3. If indexMap exists and unused glyph ID > last used glyph ID, then its major/minor number set to that of the last used glyph (removed from table)