Blind trusts are not blind at all. You choose the trustee. You can also give them initial instructions. They can give you regular updates, and you know what you put in the blind trust.
Further, for Prime Minister Carney, the holdings are actually outside the blind trust. For the Brookfield conglomerate—the 103 companies—he knows that he owns them. He knows that he owns stock options in Brookfield until 2033. He knows he's in a financial conflict of interest, and there's nothing preventing, prohibiting or penalizing it.