When a police officer stops a motorist for a minor traffic offence, typically the officer will fill out the relevant information on a form called the "certificate of offence". Underneath the certificate is a carbon copy called the "offence notice". The officer gives the offence notice (commonly called a "ticket") to the motorist, and then files the certificate of offence with the court, which has the effect of commencing proceedings against the motorist.
Is the officer entitled to change the information on the certificate of offence after giving the offence notice to the motorist, but before filing the certificate with the court?
One would assume that any changes to the offence notice could only be made if the accused is told of the changes. In a surprising, at least to me, decision the Court of Appeal says amendments can be made without notice. If this prejudices an accused they can deal with the matter at trial or on appeal.
The Court holds in York (Regional Municipality) v. Wadood, 2017 ONCA 45:
 However, for the prosecution to achieve its goal of allowing officers to correct minor errors or omissions on a certificate of offence, it is not necessary to go as far as implying an amendment power in s. 90. In my opinion, officers are entitled to change information on a certificate of offence before filing with the court, even after serving a defendant with an offence notice. Nothing in the Act or the rules precludes officers from doing so. Proceedings against a defendant have not yet commenced. And neither the Act nor the rules requires that the information on a certificate of offence be identical to the information on an offence notice before it is filed with the court.
 Allowing an officer to correct the certificate of offence before filing it with the court furthers the purpose of the Provincial Offences Act and proceedings under it. The express purpose of the Act is set out s. 2(1):
2. (1) The purpose of this Act is to replace the summary conviction procedure for the prosecution of provincial offences, including the provisions adopted by reference to the Criminal Code (Canada), with a procedure that reflects the distinction between provincial offences and criminal offences.
 This court and other judges have elaborated on this purpose. The Act is intended to permit judges to decide cases on their merits, to deal efficiently and inexpensively with the province's large volume of minor regulatory offences, and to avoid having proceedings invalidated because of technical objections or irregularities having no prejudicial impact on a defendant. See, for example, London (City) v. Young, per Doherty J.A. and Ontario (Ministry of Labour) v. Discovery Place Ltd.,  O.J. No. 690 (Ont. C.J.), varied on other grounds,  O.J. No. 1887 (Ont. C.A.).
 If officers were not permitted to correct information on a certificate of offence before filing the certificate with the court, then many proceedings under ss. 9(1) or 9.1 would be quashed simply because the officer misspelled a name, left out a name of a municipality, or incorrectly wrote down the year of the alleged offence. In all of these examples – and many other examples of minor errors or omissions on certificates of offence – the defendant charged would not be misled. Quashing the certificate of offence because of minor errors that cause no prejudice would not promote the fair administration of justice in the provincial court.
 Defendants are protected if they were misled or prejudiced by a change to information on the certificate of offence that produced a variance between the certificate and the offence notice. Where a variance comes to light, s. 90 has an important role to play in promoting the purpose of the Act.
 A variance could come to light in one of two situations: (1) at a contested trial, where the defendant puts the offence notice before the court and invites the presiding judge to compare the information on the certificate with the information on the offence notice; or (2) as in the present case, on appeal, after a conviction is registered against the defendant under ss. 9.1 or 9(1) of the statute. In the latter situation, the appeal court has wide power under s. 136 of the Provincial Offences Act to receive further evidence, which presumably could include the offence notice, even though it was not before the justice of the peace in the default proceeding.
 The judge, either at trial or on appeal, faced with a variance, would have to determine its impact. If the variance had the potential to mislead the defendant, then the judge would be justified under s. 90(2) in adjourning the trial and even ordering the prosecution to pay costs. On appeal, the judge may be justified under s. 138 in reversing a conviction or varying a penalty, or if "necessary to do so to satisfy the ends of justice", ordering a new trial.
 In his judgment in R. v. Montone, 2007 ONCJ 251,  O.J. No. 2230, at paras. 38-39, Lampkin J. gives a good example of a case where a defendant would be misled by a change to the certificate of offence and where a conviction would result in an injustice. An officer arrives at the scene of an accident and issues a certificate of offence for following too closely. The officer then calls in to report the accident to his staff sergeant who advises that the defendant should have been charged with careless driving, a more serious offence with a greater monetary penalty and more demerit points. The officer then changes the certificate of offence to record the more serious offence and files it with the court. The defendant, thinking he had been charged only with following too closely, does not dispute the charge; the justice of the peace, in the defendant's absence, examines the certificate, concludes it is complete and regular on its face, and convicts the defendant of careless driving. The defendant is notified of the conviction and appeals. As Lampkin J. notes, upholding the conviction on these facts would not be just; the defendant would have been convicted of an offence for which he received no notice whatsoever.
 But against those cases – likely few – where the defendant has been misled or prejudiced by a change to the certificate of offence, are those many cases where the change may correct clerical errors or supply missing information, and the defendant is not misled or prejudiced at all. In these cases, s. 90 preserves the validity of the proceeding.