The confusion seems to be in the writing/wording of the law. I don't know of a particular sentence/paragraph or wording that literally states that possession of a defaced or altered VIN is a crime. The law seems to assume the plate is attached to a vehicle in your possession and because of that you are in possession of stolen property unless you can prove otherwise.
Look at case law R v Smith, R v Adams, or R v Sandy
In R v Sandy Even our question falls under further encompassing law such as the Traffic Safety Act and under warrantless arrest authority:
In the case of the Traffic Safety Act, police officers are authorized to arrest without warrant only with respect to specified offences. This power is governed by s. 169, which provides:
Arrest without warrant
169 (1) A peace officer may arrest a person without warrant if the peace officer, on reasonable and probable grounds, believes that
(a) the person has committed an offence in respect of any of the provisions set out in subsection (2), and
(b) the person
(i) will continue or repeat that offence if not arrested, or
(ii) has provided the peace officer with inadequate or questionable information as to the person’s identification.
(2) For the purposes of subsection (1), the following are the provisions for which a person may be arrested without a warrant:
(a) sections 51(a) and 94 relating to the operation of a motor vehicle without having a subsisting operator’s licence;
(b) section 52(1)(a) and (d) relating to the operation of a motor vehicle without having a subsisting certificate of registration;
(c) section 53(1)(b) relating to the displaying of a licence plate other than one authorized under this Act;
(d) section 61 relating to the defacing of licence plates;
(e) section 68(2)(a) relating to possession of a motor vehicle or serially numbered part,
(i)
where a serial number or other authorized identifying number or mark is not displayed in the space provided for displaying that identification by the manufacturer, or
(ii) where the serial number has been removed, defaced, covered, altered or destroyed or become illegible;
BBM
In conclusion it appears that possession of a defaced/altered VIN
IS a contravention and an arrest can be made, assumed it is attached but defaced or missing from a vehicle altogether.
Does that help or make things worse? Seems we are drifting somewhat.
ETA.......Sorry, I forgot to add a link to the Alberta case law on a Voir Dire ruling in Respondent v Sandy 2007
http://www.canlii.org/eliisa/highli...GljbGUgSWRlbnRpZmljYXRpb24gTnVtYmVyAAAAAAAAAQ