Summary proceedings for an offence under section 65 or 66 of this Act may be brought within a period of six months from the date on which evidence sufficient in the opinion of the prosecutor to warrant the proceedings came to his knowledge; but no such proceedings shall be brought by virtue of this section more than three years after the commission of the offence.

For the purposes of this section a certificate signed by or on behalf of the prosecutor and stating the date on which such evidence as aforesaid came to his knowledge shall be conclusive evidence of that fact; and a certificate stating that matter and purporting to be so signed shall be deemed to be so signed unless the contrary is proved.