Comment by infogulch
2 days ago
Unicode wants to be able to preserve round-trip re-encoding from this other standard which has separate letter-K and degree-K characters. Making these small sacrifices for compatibility is how Unicode became the defacto world standard.
The "other standard" in this case being IBM-944. (At least looking at https://www.unicode.org/versions/Unicode1.0.0/ch06.pdf p. 574 (=110 in the PDF) I only see a mapping from U+212A to that one.)
The ICU mappings files have entries for U212A in the following files:
[flagged]
That "deeper explanation" seems incorrect, considering that the KSC column is empty in the mapping linked above.