I have just had a situation here, a good one. Buyer in Mexico was asking where his package was as it had been missing for 20 days. I gave them UR 002 665 621 CA (NO DELIVERY SCAN on Small Packet Air shipping label). He went to Correos de Mexico website and found out that it has just arrived in the country. You can check it out. CanadaPost does not give any info re this.
You can check it out yourself, i could not believe my eyes. Just to share if it could be helpful to everyone.