(1) No proceedings for an offence under section 237 may be commenced after the earlier of -
(a) the end of the period of 3 years beginning with the date of the commission of the offence, or
(b) the end of the period of 1 year beginning with the date of discovery of the offence by the prosecutor.
(2) For the purposes of subsection (1)(b) -
(a) a certificate signed by or on behalf of the prosecutor and stating the date on which the prosecutor discovered the offence is conclusive evidence of that fact, and
(b) a certificate stating that matter and purporting to be so signed is to be treated as so signed unless the contrary is proved.