I’m surprised that you were downvoted, because you’re totally right. UTF‐16 can represent almost a 21‐bit range—yes, greater than 16—thanks to surrogate pairs.

I’m surprised that you were downvoted, because you’re totally right. UTF‐16 can represent almost a 21‐bit range—yes, greater than 16—thanks to surrogate pairs. The largest codepoint representable in UTF‐16 is U+10FFFF. That’s why UTF‐8 dropped the 5‐ and 6‐byte sequences, why even UTF‐32 is limited to 21 bits, and why U+D800 to U+DFFF (the range UTF‐16 uses to encode surrogate pairs) are explicitly disallowed from being represented in UTF‐8 and UTF‐32.