[rzzzt]

I'm sort of buying and not buying this interpretation. Celsius is discussed under section "Unit symbols" in the PDF (page 8-9 of the linked Chapter 22), where the quoted "it is better" sentence appears...

...then immediately afterwards a new section named "Compatibility" starts where the use of code points that are composites of several letters, e.g. ℡ and ℻ are indeed discouraged, suggesting they be spelled out in full as TEL and FAX instead.

Do you feel ℃ falls into a continuation/overlap between these two sections?