Do you know if those characters are in supplemental planes? The BMP would only be glyphs from U+0000 through U+FFFF (though the first 32 and last two aren't printable, and wouldn't be included in this font).

Another example would be emoji, which would probably now be considered "basic" by most people but have always been in a supplemental plane.

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amake a day ago | parent [-]

Lots of the rarer CJK ideographs are outside the BMP.

	▲	runarberg a day ago \| parent [-]
		This was actually the first issue for my kanji learning app https://github.com/runarberg/shodoku/issues/1 A classic utf-16 bug, where I failed to grab the two remaining bytes of these ideographs.