Right, but my point was that the "U+10FFFF" limit hadn't been decided yet at the point where MySQL first added the "UTF-8" encoding, and it was added later, so

Right, but my point was that the "U+10FFFF" limit hadn't been decided yet at the point where MySQL first added the "UTF-8" encoding, and it was added later, so it may not have been clear to them that UTF-8 would ever be a "fixed target" so to speak. In retrospect we can see that UTF-8 has been and will continue to be static, since it's become so universally adopted.