I was a funeral director in Ontario, Canada. The law here is that the contract you sign with the crematorium will have a cremation number which will be stamped into a metal disk and that disk will be placed with the remains. After cremation, the disk will be in the cremated remains. People who receive the cremated remains can check that the number on the disk matches the number on the contract they signed.

This system stops honest mistakes but nothing stops people from intentionally swapping disks. Say a funeral home worker is filling urns with a batch of cremated remains they recieved from the crematorium. They accidentally put remains A into the urn for family B and remains B into the urn for family A. The worker should swap the remains…but swaping the disks is easier. Most people I’ve worked with would do the right thing but the system still relies on people being honest.