Unsynced quotes

While a double opening quote without a closing one is reported, a single is not. How come?
The check is not very simple, I know, because:
's is allowed as a valid sentence start (for Dutch).
’ at the start can be matched by a quote within the sentence or within the paragraph.
’ within the sentence should be matched within the sentence.

Correct examples:
's Ochtends is het koud.
's Ochtends is het ‘koud’.
‘Het is koud.’
‘Het is koud’, zei ze.
‘Het is koud. Maar het vriest niet.’

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