I think unique has a specific meaning in your context which isn't what the standard definition of unique means. There are never two people in a carrier's databa

I think unique has a specific meaning in your context which isn't what the standard definition of unique means. There are never two people in a carrier's database assigned to the same number. It can however be assigned to another person as long as it is deassigned from the previous person. The number, at any point, is always unique.