C-x 8 RET to insert a Unicode character. I enter the hex value -- for example,
201c -- and the minibuffer says "no matches". But if I just hit enter, the expected left double quote character “ gets inserted.
OTOH, if I type "left quot" or similar, the completion narrows the choices as expected, and I can use tab to complete LEFT DOUBLE QUOTATION MARK as expected.
I'm seeing similar behavior even when I start emacs with "-Q": there, I type "201c", hit tab -- it says no match, but if I hit enter, it inserts the character.
Why is the completion saying there's no matches, but hitting enter successfully finds the character?