Compiled OTF fonts have numerous characters (code-points) without defined glyphs

[DIV-on-github]

The compiled OTF fonts have numerous characters (code-points) without any defined glyphs.

This is evident when viewing the font in Windows' Character Map.
For example:
U+0080 to U+009F are blank, but I couldn't see these explicitly defined in the font.
U+0391 to U+03C9 only three glyphs are explicitly defined for Greek letters, but every character in this range is displayed by Character Map (all but three with the not-defined glyph).
U+2801 to U+28ff display Braille patterns, none of which are defined in the font.
U+3131 to U+318E display Korean characters (Hangul), none of which are defined in the font.
U+3400 to U+9FA5 display CJK ideographs (Chinese characters), none of which are defined in the font.

Although the above behaviour is strange, it also seems to be preventing the family of fonts from being being embedded into PDF files (whether using PDF/A format or not), and — in some cases — preventing text in PDF files from being persistently marked as being formatted as a Zilla Slab font.
This is detailed at length at https://forum.tracker-software.com/viewtopic.php?p=169710

—DIV

[DIV-on-github]

Actually, the two reported issues may not be so closely related as I thought.

• The behaviour with Character Map turns out to be 'normal' for many OTF fonts.
• However, the inability to embed fonts is not normal. I have logged a separate issue that may more closely reflect this.